JP2020035837A - Method of manufacturing epitaxial wafer, method of manufacturing semiconductor device, and epitaxial wafer - Google Patents

Abstract

To provide a method of manufacturing an epitaxial wafer having a current confinement layer in which variation in an amount of oxidation in a wafer surface is suppressed than before.SOLUTION: The method of manufacturing an epitaxial wafer includes the steps of: forming a semiconductor laminate including a high Al composition layer made of at least AlGaAs (0.9≤x≤1) on a substrate; forming a mesa structure exposing at least a side surface of the high Al composition layer; and oxidizing a part of the high Al composition layer from the exposed side surface of the high Al composition layer to form a current confinement layer. In the oxidation step, oxidation is performed at 480 to 580°C in an atmosphere containing water vapor at 0.001 to 0.01 g/L.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing an epitaxial wafer manufactured by using partial oxidation, a method for manufacturing a semiconductor device using the same, and an epitaxial wafer having a current confinement layer in which a high Al composition layer is partially oxidized.

  VCSELs (Vertical Cavity Surface Emitting Lasers) have been used in various applications such as optical communication, DVDs, CDs, printers, and optical mice. Attention has also been paid to 3D sensor applications. Light emitting elements that do not perform laser oscillation but have a current confinement layer, such as point light source LEDs, are also used for various sensor applications.

  Patent Document 1 discloses that a semiconductor layer stacked on a semiconductor substrate is dry-etched to form a mesa structure, and a part of the high Al composition layer is steam-oxidized from a side wall of the mesa structure by high-temperature steam from an outer peripheral side. An oxidized VCSEL in which an insulating region is formed as described above is disclosed.

  Patent Literature 2 discloses an oxidizing apparatus that prevents a wafer from being warped in a thermal oxidation process and a variation in oxidation in a wafer depending on a heater shape.

  As for the oxidation method, Patent Document 1 describes, for example, that the substrate is exposed to a steam atmosphere of 350 ° C. using nitrogen as a carrier gas for 30 minutes. Patent Document 2 describes that it is preferable to set the thermal oxidation temperature between, for example, 400 ° C. and 500 ° C.

JP-A-2004-327862 JP 2017-50389 A

  As the diameter of an epitaxial wafer (hereinafter may be abbreviated as a wafer) increases, how the characteristics in the wafer surface, that is, the variation in the amount of oxidation in the oxidation step for forming the insulating region, is suppressed. Is an issue. If the variation in the oxidation amount in the wafer surface is large, the size of the constricted shape also varies in the wafer surface. Therefore, the variation in the forward voltage of the semiconductor device obtained from the wafer among the devices becomes large, and further, the problem of reliability tends to occur. Although the planetary driving technique and temperature uniformization described in Patent Document 2 are effective for suppressing the variation in the oxidation amount, further suppression of the variation is required.

  Accordingly, an object of the present invention is to provide a method for manufacturing an epitaxial wafer having a current confinement layer in which variation in the amount of oxidation in a wafer surface is suppressed. Another object of the present invention is to provide a method for manufacturing a semiconductor device using this manufacturing method. Still another object of the present invention is to provide an epitaxial wafer having a current confinement layer in which variation in the amount of oxidation in a wafer surface is suppressed.

  In order to solve the above-mentioned problems, the present inventors diligently studied. The present inventors have recalled that the high Al composition layer to be oxidized is oxidized under conditions different from the conventionally recommended conditions of thermal oxidation in a steam atmosphere. As a result, it was found that the variation in the current confinement diameter due to the oxidation amount in the wafer surface and the variation in the forward voltage greatly affected by the current confinement diameter can be improved as compared with the conventional art. Reached.

That is, the gist configuration of the present invention is as follows.
(1) forming a semiconductor laminate including a high Al composition layer made of at least Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) on a substrate;
Forming a mesa structure exposing at least a side surface of the high Al composition layer;
Oxidizing a part of the high Al composition layer from the exposed side surface of the high Al composition layer to form a current confinement layer,
The method of manufacturing an epitaxial wafer, wherein the oxidizing step is oxidized at 480 to 580 ° C. in an atmosphere containing water vapor at 0.001 to 0.01 g / L.

(2) The method of manufacturing an epitaxial wafer according to (1), wherein in the step of forming the semiconductor laminate, a lower reflective layer, a light emitting layer, the high Al composition layer, and an upper reflective layer are sequentially formed on the substrate. .

(3) The method for producing an epitaxial wafer according to (1) or (2), wherein the temperature of the oxidation step is 510 ° C. or higher.

(4) The method for manufacturing an epitaxial wafer according to any one of (1) to (3), wherein the Al composition x of the high Al composition layer satisfies 0.9 ≦ x <1.

(5) A method for manufacturing a semiconductor device, comprising a step of dicing the epitaxial wafer obtained by the method according to any one of (1) to (4).

(6) a semiconductor laminate including a high Al composition layer made of at least Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) on a substrate of 3 inches or more;
A mesa structure in which a side surface of a current confinement layer including at least the high Al composition layer is exposed,
The high Al composition layer constitutes a current confinement layer sandwiched between oxidized regions provided on an outer peripheral side of the mesa structure,
When 19 or more constricted shapes in the wafer surface are measured while looking down on the confined region that has not been oxidized, the standard of the width of the crystal orientation <01-1> and the width of the crystal orientation <010> of the constricted shape is measured. An epitaxial wafer having a deviation of 0.6 μm or less.

In this specification, the crystal orientation
Is expressed as a crystal orientation <01-1>.

(7) the constriction shape is circular;
The epitaxial wafer according to (6), wherein the average of the ratio of the width of the crystal orientation <010> to the width of the crystal orientation <01-1> is 100 to 102%.

  According to the present invention, it is possible to provide a method for manufacturing an epitaxial wafer having a current confinement layer in which variation in the amount of oxidation in a wafer surface is suppressed more than conventionally. Further, the present invention can provide a method for manufacturing a semiconductor device using this manufacturing method. Further, the present invention can provide an epitaxial wafer having a current confinement layer in which variation in the amount of oxidation in a wafer surface is suppressed.

FIG. 4 is a diagram illustrating a manufacturing process of the surface emitting laser according to the embodiment of the present invention. It is a schematic diagram of an example of a steam oxidation device applicable to the manufacturing method of the present invention. It is a schematic diagram which shows 19 measurement places in the wafer surface when measuring the constriction shape of the epitaxial wafer of this invention. It is a typical example of an infrared camera photograph at the time of measuring a stenosis diameter in an Example. 4 is a graph showing a relationship between an Al composition and an oxidation rate in Examples. 4 is a graph showing a relationship between an Al composition and an oxidation rate in Examples. 4 is a graph showing a variation of a forward voltage Vf in a wafer surface in the example.

(Method of manufacturing epitaxial wafer)
The present invention is applied to an epitaxial wafer for obtaining a semiconductor device having a semiconductor laminate including a high Al composition layer. Specifically, the high Al composition layer sandwiched between a plurality of semiconductor layers in the thickness direction of the substrate is partially oxidized by oxidizing from the side surface, and the high Al composition layer is oxidized in the in-plane direction of the substrate. The present invention relates to a technique for forming a current confinement layer sandwiched between layers. A semiconductor device can be obtained by dicing the obtained epitaxial wafer. What kind of layer sandwiches the high Al composition layer in the thickness direction of the substrate is arbitrary, and can take various forms.

<Semiconductor device and surface emitting laser as its mode>
Hereinafter, in the present embodiment with reference to the reference numerals in FIG. 1, as an example of the semiconductor device 1, a lower reflective layer 20, a light emitting layer 30, and Al _x Ga _{1 -x} As (0.9 ≦ x ≦ A surface emitting laser in which a current confinement layer 40 including a high Al composition layer 41 of 1) and an upper reflection layer 50 are sequentially formed will be described.

The method for manufacturing an epitaxial wafer according to the present invention is directed to a semiconductor laminated body including at least a high Al composition layer 41 made of Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) on a substrate 10 (in FIG. 20, 30, 41, 50) (Step A in FIG. 1), a step of forming a mesa structure exposing at least the side surface of the high Al composition layer 41 (Step B in FIG. 1), and a high Al composition layer 41. An oxidation step of oxidizing a part of the high Al composition layer 41 from the exposed side surface to form the current confinement layer 40 (Step C in FIG. 1). By the oxidation treatment, the high Al composition layer 41 is sandwiched between the oxidized regions 42 provided on the outer peripheral side of the mesa structure to form the current confinement layer 40. Then, as described in detail later, in the oxidation step (Step C in FIG. 1), oxidation treatment is performed at 480 to 580 ° C. in an atmosphere containing 0.001 to 0.010 g / L of water vapor. Further, as shown in Step D of FIG. 1, an upper electrode 61 may be provided on the upper reflective layer 50, and a lower electrode 62 may be provided on the back surface of the substrate 10. The semiconductor element 1 can be obtained by dicing the thus obtained epitaxial wafer having the semiconductor element structure.

  FIG. 1 shows only a specific example of the surface emitting laser, and the position of the high Al composition layer 41 to which the manufacturing method of the present invention is applied is not limited to the above example of the surface emitting laser. The high Al composition layer 41 can be provided between the lower reflective layer 20 and the light emitting layer 30, and various layers can be sandwiched between the high Al composition layer 41 and the front and back (in the vertical direction on the paper of FIG. 1). Further, the present manufacturing method is used to obtain a point light source LED having no upper reflective layer, such as a semiconductor light emitting device having a lower reflective layer, a lower clad layer, a light emitting layer, a current confinement layer, and an upper clad layer provided on a substrate. The present invention may be applied to a current confinement type LED having no reflective layer on both the upper and lower sides. The present manufacturing method may be applied not only to a semiconductor light emitting element but also to a semiconductor light receiving element. The reflection layers (the lower reflection layer 20 and the upper reflection layer 50) are layers provided for reflecting light emitted from the light emitting layer 30. As such a reflective layer, a black reflective layer (DBR) in which AlGaAs layers having different Al compositions (see reference numerals 21 and 22 and 51 and 52) are alternately and repeatedly laminated, or a metal reflective layer can be used.

  Hereinafter, each step of the manufacturing method of the present invention will be sequentially described.

<Step of forming semiconductor laminate>
First, as shown in FIG. 1 step A, a semiconductor laminate including a high Al composition layer 41 made of at least Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) is formed on a substrate 10.

<<<< composition of high Al composition layer >>
The high Al composition layer 41 is made of Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1), and more preferably 0.9 ≦ x <1. The value of the Al composition x can be measured using SIMS or TEM-EDS. When the Al composition x is less than 0.9, the difference in oxidation rate between the high Al composition layer and another semiconductor layer is small, and it becomes difficult to selectively oxidize the high Al composition layer 41. As a result, the current confinement layer 40 Is also difficult to form. In the case of AlAs (that is, x = 1), the present invention can suppress the variation of the oxidation amount in the wafer surface, but the influence of the plane orientation remains strong (for example, even if the mesa shape is circular, the constriction shape approaches a square). Tend. Therefore, when it is desired to make not only the amount of oxidation but also the shape uniform, it is preferable that 0.9 ≦ x <1, and more preferably, for example, 0.9 ≦ x ≦ 0.98.

<Composition of semiconductor layer other than high Al composition layer>
As for the semiconductor layers other than the high Al composition layer 41, it is preferable to use a semiconductor layer having a lower Al composition than the high Al composition layer 41 and less susceptible to oxidation than the high Al composition layer 41. Such a semiconductor layer may be any layer that can be grown by sandwiching the current constriction layer 40 in the thickness direction in epitaxial growth, and may be, for example, AlGaAs, AlInGaP, InGaAs, AlInP, or InGaP.

<Substrate>
The substrate 10 refers to a growth substrate used for epitaxial growth. After epitaxial growth of the semiconductor laminate on the growth substrate 10, an arbitrary substrate for support may be joined onto the semiconductor laminate to remove the substrate 10 used for growth. As such a substrate 10, an InP substrate can be used in addition to a GaAs substrate. As the diameter of the wafer increases, it becomes an issue how to suppress the variation in the characteristics within the wafer surface, that is, the variation in the oxidation amount in the oxidation step. Therefore, the substrate to which the manufacturing method of the present invention is preferably applied is 3 inches or more.

<Step of Forming Mesa Structure Exposing Side of High Al Composition Layer>
Next, as shown in Step B of FIG. 1, a mesa structure for exposing the side surface of the high Al composition layer 41 is formed. A side surface of the high Al composition layer is exposed by forming a mesa structure having a specific shape and an arrangement pattern on the semiconductor laminate including the high Al composition layer 41. In order to form a mesa structure, a general method such as photolithography may be applied.

  As the shape of the semiconductor laminate after the formation of the mesa structure, the shape of the semiconductor laminate viewed from above can be a circle, a polygon such as a square or a hexagon, and the aspect ratio is changed like a rectangle. Is also good. Furthermore, the case where the periphery is removed so as to expose all the side surfaces of the current constriction layer 40 of the semiconductor laminate after the formation of the mesa structure, and the case where a part of the side surface of the high Al composition layer is left unexposed and In some cases, a concave groove having a gap is formed. In any case, the mesa structure is sufficient as the high Al composition layer is oxidized so that the steam can sufficiently touch the side surface of the high Al composition layer.

<Oxidation step of oxidizing a part of the high Al composition layer from the exposed side surface of the high Al composition layer>
Following the step of forming the mesa structure, an oxidation step is performed (Step C in FIG. 1). This step is a step of oxidizing a high Al composition layer of Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1). When the oxidation produces a complex oxide containing an insulating Al oxide as a main component, Conceivable. This oxidation step is an oxidation step performed using water vapor, and is performed in an atmosphere containing 0.001 to 0.01 g / L of water vapor, and preferably 0.008 g / L or less. In addition, a gas containing 0.001 to 0.01 g / L of steam is used at 10 to 30 L / min at a rate of 10 to 30 L / min so that the water vapor content in the atmosphere around the high Al composition layer 41 during the oxidation step does not greatly change. It is more preferable to keep flowing toward. It is more preferable that the gas containing 0.001 to 0.01 g / L of water vapor contains water vapor in an inert gas such as nitrogen or argon in order to secure reproducibility of the oxidation rate.

  The inventors anticipate that whether the oxidation rate is rate-limiting or reaction-limited is related to the water vapor concentration of the present invention. When the water vapor concentration is 0.01 g / L or less, the oxidation rate is mainly controlled by the supply, and the influence of the variation in the reaction rate due to the variation in temperature on the oxidation rate is reduced. On the other hand, if the concentration of water vapor exceeds 0.01 g / L, the supply becomes sufficient and the oxidation rate becomes the reaction rate-determining, and it is expected that the variation in the reaction rate caused by the temperature variation will have an excessive effect on the oxidation rate. . It is expected that the influence of crystal anisotropy (the effect that the reaction rate varies depending on the crystal orientation) may be reduced under the conditions that control the supply. If the concentration of water vapor is less than 0.001 g / L, the oxidation rate is too small and the time required for the oxidation step becomes too long, which is not practical as a production step. / L.

  The temperature at which the oxidation treatment is performed (stage temperature) is suitably higher than the temperature which is conventionally regarded as appropriate, and the oxidation is performed at 480 to 580 ° C, and preferably at 510 to 580 ° C. Since it is difficult to accurately measure the surface temperature of the semiconductor laminate during the oxidation process, the stage temperature (set temperature) immediately after the oxidation process after mounting the wafer is set to the temperature of the oxidation process. I do. If the stage temperature is lower than 480 ° C., the oxidation rate is too small and the time required for the oxidation step becomes too long at the above-mentioned water vapor concentration, which is not practical as a production step. On the other hand, if the stage temperature exceeds 580 ° C., the oxidation rapidly occurs, so that the semiconductor layers other than the high Al composition layer which is not supposed to be oxidized have a large influence, and there is a possibility that adverse effects such as surface roughening of the semiconductor laminate may occur. Occurs. In addition, the oxidation time in this step may be appropriately set according to the steam concentration and the temperature at which the oxidation treatment is performed (stage temperature) according to the required constriction shape. Although not intended to be limiting, for example, the oxidation time can be between 10 minutes and 3 hours.

  FIG. 2 shows a configuration example of the steam oxidation apparatus 100 for performing such an oxidation step. A mechanism 110 for supplying a fixed amount of water by a mass flow controller and supplying a steam heated to 100 degrees or more (for example, 180 degrees) in a pure water vaporizer with a constant amount of steam, and preheating the steam (for example, 120 degrees) A) a mechanism 120 for feeding the wafer W to the stage using an inert gas such as nitrogen gas, a mechanism (not shown) for transferring and collecting the wafer W on the stage, and a mechanism 130 for heating the stage to a specific temperature (stage temperature). And Further, in order to reliably stop the oxidation of the high Al composition layer for the oxidation time from the start of supplying the gas containing water vapor to the wafer on the stage until the supply is stopped, the gas containing water vapor is stopped. Also, a mechanism 140 for spraying a gas containing no water vapor on the wafer may be provided. FIG. 2 also shows an outlet 150 for discharging the gas introduced into the chamber.

  By dicing the epitaxial wafer obtained through each of the above steps, a semiconductor element can be obtained. Prior to dicing, as shown in Step D of FIG. 1, an upper electrode 61 may be provided on the upper reflective layer 50, and a lower electrode 62 may be provided on the back surface of the substrate 10 as described above. is there. The form of the electrode is not limited to this example at all, and may be provided as appropriate depending on the mode of the semiconductor element.

<Epitaxial wafer>
Reference is made to the reference numerals in FIG. The epitaxial wafer obtained by the above-described manufacturing method has a semiconductor laminate including a high Al composition layer 41 made of at least Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) on a substrate 10 of 3 inches or more. . Then, the current confinement layer 40 is constituted by the oxidized region 42 sandwiching the high Al composition layer 41 in the same plane as the high Al composition layer 41. The epitaxial wafer has a mesa structure in which the side surface of the current confinement layer 40 is exposed, and the variation of the oxidation amount of the current confinement layer 40 in the wafer surface can be suppressed. Here, that the variation in the oxidation amount in the wafer surface is suppressed, that is, in the non-oxidized narrow region of the current narrowing layer 40, at least 19 measurement points in the wafer surface have a narrow crystal. When the width of the orientation <01-1> and the width of the crystal orientation <010> are measured, it means that the standard deviation of the width of each crystal orientation is small and the standard deviation is 0.6 μm or less. More preferably, the standard deviation is 0.4 μm or less.

  When the orientation flat (OF) of the substrate used is the (011) plane in the crystal orientation of the zinc blende type semiconductor crystal having the (100) plane as the upper surface, the crystal orientation <01-1> is OF horizontal. The crystal orientation <010> corresponds to a direction inclined by 45 degrees with respect to the OF.

<Method of measuring non-oxidized region (constriction shape) of current confinement layer>
19 or more measurement points in the wafer surface is assumed to have the position of the 19 locations shown in FIG. 3 including the center P ₁ of the wafer surface (P ₁ to P _19). When measuring more than 19 points, a position that does not overlap with the 19 points shown in FIG. 3 is selected as a measurement point. Position of the measuring points P ₁ to P ₁₉ are determined as follows.

First, the wafer center and the point P _1. In a straight line passing through the OF and parallel and point P _1, defined as the distance L ₁ point inside the two points respectively P _2, P ₃ from the wafer edge. Next, the vertices of each side of the square including the side parallel to the OF and the length of each side being L ₂ and the points obtained by dividing each side into three equal parts are clockwise P ₄ , P ₅ ,. Determined as ₁₅ . Further, the vertices of each side of a square including a side parallel to the OF and having a length of one side of L ₃ are defined as P ₁₆ , P ₁₇ , P ₁₈ , and P ₁₉ in a clockwise direction. The distances L ₁ , L ₂ and L ₃ are respectively 5/76, 11/20 and 11/64 of the wafer diameter.

  As a method for measuring the stenosis shape, an image may be taken from a position overlooking the stenosis shape using, for example, an infrared camera, utilizing the fact that the transmittance changes due to oxidation. By observing the captured image, the size of the non-oxidized region (constricted shape) of the current confinement layer can be measured from the contrast difference between the oxidized region and the non-oxidized region.

<About the shape of the non-oxidized region (constriction shape) of the current confinement layer>
Similarly to the mesa structure, the non-oxidized region (constriction shape) of the current confinement layer can have a polygonal shape such as a circle, a quadrangle or a hexagon when the semiconductor laminate is viewed from above, and a rectangular shape. The aspect ratio may be changed as follows.

<Reducing anisotropy>
According to the manufacturing method of the present invention, the shape accuracy of the non-oxidized region of the current constriction layer 40 (constriction shape), that is, the high Al composition layer 41 is improved. When the specific pattern of the mesa structure is circular and the current confinement layer 40 including the high Al composition layer 41 of AlxGa1-xAs (0.9 ≦ x <1) is formed, the constriction shape also becomes circular. The average of the ratio of the width (diameter of the constriction shape) of the crystal orientation <010> to the width (diameter of the constriction shape) of the crystal orientation <01-1> in the circle is 100 to 102%, which is higher than the conventional one. Precision can be achieved. It is preferable that both the mesa structure and the constricted shape are circles having no distortion, because the current spreads easily uniformly and the efficiency as a semiconductor element can be increased. In the following examples, the diameter of the stenosis shape is also described as the stenosis diameter.

  Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1]
A 3-inch n-type GaAs substrate was prepared. Next, 46 pairs of pairs of Al _0.86 Ga _0.14 As (70 nm) and Al _0.06 Ga _0.94 As (60 nm) are repeatedly laminated on the GaAs substrate (100) surface by MOCVD to form a lower part having a total film thickness of 6 μm. The reflection layer (lower DBR) was grown. On the lower reflective layer, a crystal of In _0.23 Ga _0.77 As was grown as a light emitting layer with a thickness of 30 nm, and then a crystal of Al _0.963 Ga _0.037 As was grown as a high Al composition layer with a thickness of 30 nm. An upper reflection layer (upper DBR) having a total film thickness of 2.3 μm is formed by repeatedly stacking 18 pairs of Al _0.86 Ga _0.14 As (70 nm) and Al _0.06 Ga _0.94 As (60 nm) on the high Al composition layer. Crystals were grown.

  Next, a resist was applied to the upper surface of the upper reflective layer, and a resist mask in which circles having a diameter of 50 μm were arranged in a pattern in which the circles having a diameter of 50 μm were arranged vertically and horizontally at intervals of 220 μm was formed by photolithography. Thereafter, a region not masked by the resist mask was etched by a dry etching apparatus until a part of the lower reflective layer was exposed from the upper reflective layer. As a result, a mesa structure in which a part of the upper reflective layer, the high Al composition layer, the light emitting layer, and the lower reflective layer were arranged in a specific pattern in a cylindrical shape was produced. The side wall of the high Al composition layer was exposed as the outer periphery of the cylinder. State.

  Subsequently, an oxidation treatment was performed using a steam oxidation device. In the oxidation treatment, a layer having a large Al composition ratio (corresponding to a high Al composition layer and a part of the lower reflection layer and the upper reflection layer in the first embodiment) is moved from the cylindrical side wall toward the center of the cylinder. Oxidized. In the steam oxidation apparatus, 180 ° C steam produced in a pure water vaporizer is mixed with 120 ° C nitrogen gas, and the above mesa structure of a wafer mounted on a stage heated to 540 ° C in a processing chamber. Sprayed. At this time, the pressure of the processing chamber was set to normal pressure, the steam flow was adjusted to 0.1 g / min, and the gas flow rate of the nitrogen gas was adjusted to 20 L / min, so that the steam concentration of the gas to be blown was 0.005 g / min. L, so that the water vapor content in the atmosphere around the high Al composition layer was 0.005 g / L. The oxidation process was performed for 110 minutes, the supply of the gas containing water vapor was stopped, and the nitrogen gas at 25 ° C. was sprayed on the mesa structure of the wafer to stop the oxidation process.

  Subsequently, the oxidation amount of the wafer after the oxidation treatment was measured. Using an infrared camera, the mesa diameter (outer diameter) and the diameter of the non-oxidized area were set at 19 places in the wafer surface (the position shown in FIG. 3 with the OF being downward in the drawing) from the upper reflective layer side. (Stenosis diameter) was measured.

Since the resist mask is circular, the mesa shape formed by dry etching is circular, and the mesa diameter corresponds to the diameter of the circle. Therefore, the mesa diameter was measured using the orientation flat (011 plane) of the substrate and the diameter in the horizontal direction as representative values. Regarding the constriction diameter due to oxidation, not only the diameter in the <01-1> direction (horizontal constriction diameter) that is horizontal to the orientation flat (horizontal constriction diameter), but also the diameter in the <010> direction (diagonal constriction) inclined 45 ° with respect to the orientation flat. Diameter) was also measured.
The stenosis diameter was observed using an infrared camera (C9597-42U manufactured by Hamamatsu Photonics). In order to cause a contrast difference between the oxidized region and the non-oxidized region, the diameter (constriction diameter) was measured by the built-in function of measuring the distance between two points. Of the infrared camera photographs in measuring the confinement diameter, shown in FIG photographs of the point P ₁₆ and the point P ₄ as a representative example. Note that the dark portion at the center of each photograph is a non-oxidized region, and the light portion surrounding the dark portion is an oxidized region.

[Example 2]
The procedure was the same as in Example 1, except that the time for the oxidation treatment was changed to 100 minutes.

[Example 3]
The procedure was the same as in Example 1, except that the oxidation time was set to 40 minutes.

[Comparative Example 1]
In the oxidation treatment, the steam concentration of the gas to be sprayed is adjusted to 0.06 g / L per minute by adjusting the steam flow rate to 1.2 g / min and the gas flow rate of the nitrogen gas to 20 L / min. Was adjusted to 0.06 g / L, the stage temperature was set to 520 ° C., and the oxidation treatment time was set to 29 minutes and 40 seconds (29.7 minutes). Also, of the infrared camera photographs in measuring the confinement diameter, shown in FIG photographs of the point P ₁₆ and the point P ₄ as a representative example.

[Comparative Example 2]
In the oxidation treatment, the steam concentration of the gas to be sprayed is adjusted to 0.06 g / L per minute by adjusting the steam flow rate to 1.2 g / min and the gas flow rate of the nitrogen gas to 20 L / min. Was made in the same manner as in Example 1 except that the water vapor content was 0.06 g / L and the oxidation treatment time was 15 minutes.

[Comparative Example 3]
In the oxidation treatment, by adjusting the steam flow rate to 0.4 g / min and the gas flow rate of the nitrogen gas to 20 L / min, the water vapor concentration of the gas to be blown is set to 0.02 g / L per minute, thereby reducing the atmosphere around the high Al composition layer. Example 2 was carried out in the same manner as in Example 1 except that the water vapor content was 0.02 g / L and the oxidation treatment time was 40 minutes.

  Table 1 shows the results of evaluating the stenosis diameter due to oxidation by the oxidation treatment according to Examples 1 to 3 and Comparative Examples 1 to 3. As for the horizontal stenosis diameter (μm) and the oblique stenosis diameter (μm) in the table, the average value and the standard deviation (σ) of the 19 locations shown in FIG. 3 are shown, respectively. Are shown in Table 1 as “oblique / horizontal” (%).

  From the results in Table 1, the oxidation treatment time is longer in Examples 1 to 3 than in Comparative Examples 1 to 3, but the value of the standard deviation (σ) indicating the variation in the stenosis diameter is small. Therefore, in Examples 1 to 3, it was found that the variation of the oxidation amount in the wafer surface can be suppressed. In addition, since the ratio of oblique / horizontal is close to 100%, it was found that oxidation can be performed more isotropically (with the effect of anisotropy suppressed) on the mesa shape.

(Evaluation 1: Evaluation of difference in oxidation rate depending on Al composition)
In the above Example 1 and Comparative Example 1, Al _0.963 Ga _0.037 As was grown to a thickness of 30 nm and then oxidized to form a current confinement layer. Instead, a sample in which the current confinement layer is formed of Al _0.976 Ga _0.024 As and a sample in which the current confinement layer is formed of AlAs are prepared, and the current confinement layer is formed at the center of the wafer (point P _{1 in} FIG. 3). The oxidation rate (= (mesa diameter−constriction diameter) / 2 / treatment time) due to the difference in Al composition was measured. FIG. 5 shows the result of the oxidation treatment at 520 ° C. at a steam concentration of 0.06 g / L · min, and FIG. 6 shows the result of the oxidation treatment at 540 ° C. at a steam concentration of 0.005 g / L · min.

  From the graphs of FIGS. 5 and 6, it was found that when the oxidation treatment was performed according to the present manufacturing method, the change in the oxidation rate due to the Al composition difference could be slightly reduced. This may have led to suppression of the variation in the stenosis diameter in Table 1.

(Evaluation 2: Evaluation of forward voltage)
With respect to the wafer after the oxidation treatment, a metal layer made of Au / Zn was vapor-deposited on the upper reflection layer, and an annealing treatment was performed at 460 ° C. to form an upper electrode. Thereafter, a metal layer made of Au / Ni / Ge was deposited on the back surface of the GaAs substrate to form a back electrode, and an annealing process at 410 ° C. was performed to form a back electrode.

  A portion where the lower reflective layer of the mesa structure was exposed was cut using a dicer, and divided into individual surface emitting laser chips. The chip was mounted on a metal stem using a silver paste, and wire bonding was performed on the upper electrode using a gold wire.

  Using a constant current voltage measuring device, the forward voltage when a current of 10 mA was passed was measured at equal intervals in the radial direction from the center of the wafer on the wafer surface to the outer periphery of the wafer over 10 locations (horizontal direction of the orientation flat). FIG. 7 shows the measurement results in Comparative Example 1, Comparative Example 3, and Example 1.

  From FIG. 7, it was confirmed that, as in the oxidation step in the manufacturing method of the present invention, the variation in the forward voltage in the wafer surface can be reduced by reducing the water vapor concentration.

  ADVANTAGE OF THE INVENTION According to this invention, the fluctuation | variation of the oxidation amount in a wafer surface is suppressed more conventionally, and the semiconductor element, such as a surface emitting laser with a stable quality with little fluctuation | variation of a constriction shape, can be provided.

DESCRIPTION OF SYMBOLS 1 Semiconductor element 10 Substrate 20 Lower reflective layer 30 Light emitting layer 40 Current confinement layer 41 High Al composition layer 42 Oxidation area 50 Upper reflective layer 100 Steam oxidation device

Claims (7)

Forming a semiconductor laminate including a high Al composition layer made of at least Al _x Ga _{1 -x} As (0.9 ≦ x ≦ 1) on a substrate;
Forming a mesa structure exposing at least a side surface of the high Al composition layer;
Oxidizing a part of the high Al composition layer from the exposed side surface of the high Al composition layer to form a current confinement layer,
The method of manufacturing an epitaxial wafer, wherein the oxidizing step is oxidized at 480 to 580 ° C. in an atmosphere containing water vapor at 0.001 to 0.01 g / L.   The method of manufacturing an epitaxial wafer according to claim 1, wherein in the step of forming the semiconductor laminate, a lower reflective layer, a light emitting layer, the high Al composition layer, and an upper reflective layer are sequentially formed on the substrate.   The method for producing an epitaxial wafer according to claim 1, wherein the temperature of the oxidation step is 510 ° C. or higher.   The method of manufacturing an epitaxial wafer according to claim 1, wherein an Al composition x of the high Al composition layer satisfies 0.9 ≦ x <1. 5.   A method for manufacturing a semiconductor device, comprising a step of dicing an epitaxial wafer obtained by the manufacturing method according to claim 1. A semiconductor laminate including a high Al composition layer made of at least Al _x Ga _1-x As (0.9 ≦ x ≦ 1) on a substrate of 3 inches or more;
A mesa structure in which a side surface of a current confinement layer including at least the high Al composition layer is exposed,
The high Al composition layer constitutes a current confinement layer sandwiched between oxidized regions provided on an outer peripheral side of the mesa structure,
When 19 or more constricted shapes in the wafer surface are measured while looking down on the confined region that has not been oxidized, the standard of the width of the crystal orientation <01-1> and the width of the crystal orientation <010> of the constricted shape is measured. An epitaxial wafer having a deviation of 0.6 μm or less. The constriction shape is circular,
The epitaxial wafer according to claim 6, wherein an average of a ratio of a width of the crystal orientation <010> to a width of the crystal orientation <01-1> is 100 to 102%.