JP2023123638A - epitaxial wafer - Google Patents

Abstract

To provide a manufacturing method for an epitaxial wafer having a current narrowing layer in which the variation of the amount of oxidation within the wafer surface is suppressed more than before.SOLUTION: The manufacturing method for an epitaxial wafer includes a step for forming a semiconductor laminated body including a high Al composition layer including at least AlxGa1-xAs (0.9≤x≤1) on a substrate, a step for forming a mesa structure to expose at least the side surface of the high Al composition layer, and an oxidation step for forming a current narrowing layer by oxidizing a portion of the high Al composition layer from the exposed side surface of the high Al composition layer. In the oxidation step, the oxidation process is performed in an atmosphere including 0.001 to 0.01 g/L of water vapor at 480 to 580°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method of manufacturing an epitaxial wafer using partial oxidation, a method of manufacturing a semiconductor device using the same, and an epitaxial wafer having a current constriction layer formed by partially oxidizing a high Al composition layer.

Vertical Cavity Surface Emitting Lasers (VCSELs) have been used in various applications such as optical communications, DVDs, CDs, printers, and optical mice. It is also attracting attention as a 3D sensor application. A light-emitting element such as a point light source LED that does not oscillate but has a current constriction layer is also used for various sensor applications.

In Patent Document 1, a semiconductor layer laminated on a semiconductor substrate is dry-etched to form a mesa structure. An oxidized VCSEL is disclosed in which an insulating region is formed by sintering.

Japanese Unexamined Patent Application Publication No. 2002-100001 discloses an oxidation apparatus that prevents variations in oxidation within a wafer that depend on the warp of the wafer and the shape of the heater in the thermal oxidation process.

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

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

As the diameter of epitaxial wafers (hereinafter sometimes abbreviated as wafers) becomes larger, how to suppress variations in the characteristics within the wafer surface, that is, the amount of oxidation in the oxidation process for forming the insulating region? is an issue. If the variation in the amount of oxidation within the wafer surface is large, the size of the narrowed shape also varies within the wafer surface. Therefore, the forward voltage of the semiconductor devices obtained from the wafer varies greatly among the devices, and reliability problems are more likely to occur. Although the planetary drive technology and temperature uniformity described in Patent Document 2 are effective in suppressing variation in the amount of oxidation, further suppression of variation is required.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method of manufacturing an epitaxial wafer having a current confinement layer that suppresses variations in the amount of oxidation within the wafer surface. Another object of the present invention is to provide a method of manufacturing a semiconductor device using this manufacturing method. A further object of the present invention is to provide an epitaxial wafer having a current confinement layer that suppresses variations in the amount of oxidation within the wafer surface.

In order to solve the above problems, the present inventors have made extensive studies. Then, the present inventors imagined that the high Al composition layer to be oxidized should be oxidized under conditions different from the conventionally recommended conditions for thermal oxidation in a water vapor atmosphere. As a result, it was found that the variation in the current confinement diameter due to the amount of oxidation in the wafer surface and the variation in the forward voltage value, which is greatly affected by the current confinement diameter, can be improved more than in the past. Arrived.

That is, the gist and configuration of the present invention are 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 that exposes at least the side surface of the high Al composition layer;
an oxidation step of forming a current constriction layer by oxidizing a portion of the high Al composition layer from the exposed side surface of the high Al composition layer;
A method for producing an epitaxial wafer, wherein in the oxidation step, oxidation treatment is performed at 480 to 580° C. in an atmosphere containing 0.001 to 0.01 g/L of water vapor.

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

(4) The method for producing an epitaxial wafer according to any one of (1) to (3) above, 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 manufacturing method according to any one of (1) to (4).

(6) having 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 is provided on the outer peripheral side of the mesa structure and sandwiched between oxidized regions in the same plane as the high Al composition layer to constitute a current constriction layer;
When 19 or more constricted shapes in the wafer surface are measured by overlooking the constricted region that is not oxidized, the width of the crystal orientation <01-1> and the width of the crystal orientation <010> of the constricted shape are standardized. An epitaxial wafer, wherein all deviations are 0.6 μm or less.

を、結晶方位＜０１－１＞と表記する。 In this specification, the crystal orientation

is represented as crystal orientation <01-1>.

(7) the constriction shape is circular;
The epitaxial wafer according to (6) above, wherein an average 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 of manufacturing an epitaxial wafer having a current confinement layer that suppresses variations in the amount of oxidation within the wafer surface compared to conventional methods. Moreover, the present invention can provide a method for manufacturing a semiconductor device using this manufacturing method. Furthermore, the present invention can provide an epitaxial wafer having a current confinement layer that suppresses variations in the amount of oxidation within the wafer surface.

FIG. 4 is a diagram explaining a manufacturing process of a surface emitting laser according to one embodiment of the present invention; 1 is a schematic diagram of an example of a steam oxidation apparatus applicable to the manufacturing method of the present invention; FIG. FIG. 4 is a schematic diagram showing 19 measurement points in the wafer surface when measuring the constriction shape of the epitaxial wafer of the present invention. It is a representative example of an infrared camera photograph when the constriction diameter was measured in Examples. 4 is a graph showing the relationship between Al composition and oxidation rate in Examples. 4 is a graph showing the relationship between Al composition and oxidation rate in Examples. 5 is a graph showing variations in forward voltage Vf within the wafer plane in the example.

(Method for manufacturing epitaxial wafer)
INDUSTRIAL APPLICABILITY 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 it 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. The layers sandwiching the high Al composition layer in the thickness direction of the substrate are arbitrary and can take various forms.

<Semiconductor device and surface-emitting laser as an aspect thereof>
Hereinafter, referring to the symbols in FIG. 1, in this embodiment, as an example of the semiconductor device 1, a lower reflective layer 20, a light emitting layer 30, Al _x Ga _1-x As (0.9≦x≦ 1) in which the current blocking layer 40 including the high Al composition layer 41 and the upper reflective layer 50 are formed in this order.

The method for manufacturing an epitaxial wafer _according to the present invention comprises a semiconductor laminate (in _the example of FIG. 1, the symbol 20, 30, 41, 50) (FIG. 1 step A), forming a mesa structure exposing at least the side surface of the high Al composition layer 41 (FIG. 1 step B), and forming the high Al composition layer 41 has an oxidation step of forming the current confinement layer 40 by oxidizing a part of the high Al composition layer 41 from the exposed side surface of the (FIG. 1 step C). 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 constitute the current confinement layer 40 . Then, as will be described later in detail, 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. Also, as shown in step D of FIG. By dicing the epitaxial wafer having the semiconductor device structure thus obtained, the semiconductor device 1 can be obtained.

Note that FIG. 1 merely shows a specific example of a 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 example of the surface emitting laser. A 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 before and after the high Al composition layer 41 (in the vertical direction of the paper surface of FIG. 1). In addition, this manufacturing method is used to obtain a point light source LED that does not have an 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 blocking layer, and an upper clad layer on a substrate. It can also be applied to current confinement type LEDs that do not have reflective layers on the top and bottom. This manufacturing method may be applied not only to the semiconductor light emitting device but also to the semiconductor light receiving device. The reflective layers (lower reflective layer 20 and upper reflective layer 50 ) are layers provided to reflect light emitted from the light emitting layer 30 . As such a reflective layer, a black reflective layer (DBR) in which AlGaAs layers (reference numerals 21, 22 and 51, 52) with different Al compositions are alternately and repeatedly laminated, or a metal reflective layer can be used.

Hereinafter, each step of the production method of the present invention will be described in order.

<Step of Forming Semiconductor Laminate>
First, as shown in step A of FIG. 1, a semiconductor laminate including at least a high Al composition layer 41 made of 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), more preferably 0.9≦x<1. The value of 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 the other semiconductor layers is small, making selective oxidation of the high Al composition layer 41 difficult. is also difficult to form. In the case of AlAs (that is, x=1), although the present invention can suppress variations in the amount of oxidation within the wafer surface, the effect of the plane orientation remains strong (for example, even if the mesa shape is circular, the constriction shape approaches a square shape). Tend. Therefore, when it is desired to make not only the amount of oxidation but also the shape uniform, 0.9≦x<1 is preferable, and for example, 0.9≦x≦0.98 is more preferable.

<Composition of semiconductor layer other than high Al composition layer>
Semiconductor layers other than the high Al composition layer 41 preferably have a lower Al composition than the high Al composition layer 41 and are more resistant to oxidation than the high Al composition layer 41 . Such a semiconductor layer may be a layer that can be grown while sandwiching the current confinement layer 40 in the thickness direction during epitaxial growth, and may be, for example, AlGaAs, AlInGaP, InGaAs, AlInP, or InGaP.

<Substrate>
Substrate 10 refers to a growth substrate used for epitaxial growth. After epitaxially growing the semiconductor laminate on the substrate 10 for growth, any supporting substrate may be bonded onto the semiconductor laminate and the substrate 10 used for growth may be removed. As such a substrate 10, an InP substrate can be used in addition to a GaAs substrate. As the diameter of the wafer increases, the problem becomes how to suppress variations in the characteristics within the wafer surface, that is, the amount of oxidation in the oxidation process. Therefore, the substrate to which the manufacturing method of the present invention is preferably applied has a size of 3 inches or more.

<Step of Forming Mesa Structure Exposing Sides of High Al Composition Layer>
Next, as shown in step B of FIG. 1, a mesa structure is formed to expose the side surfaces of the high Al composition layer 41 . By forming a mesa structure having a specific shape and arrangement pattern in the semiconductor laminate including the high Al composition layer 41, the side surface of the high Al composition layer is exposed. A general technique such as photolithography may be applied to form the mesa structure.

After forming the mesa structure, the semiconductor laminate may have a shape such as a circle, a polygon such as a quadrangle or a hexagon, or a rectangular shape with a different aspect ratio. good too. Furthermore, in the case where the periphery is removed so as to expose all the side surfaces of the current confinement layer 40 of the semiconductor laminate after the formation of the mesa structure, and in the case where the side surfaces of the high Al composition layer are partially left unexposed, a predetermined In some cases, concave grooves are formed with spaced-apart gaps. In either case, the mesa structure should be such that the side surfaces of the high Al composition layer can be sufficiently contacted by water vapor to oxidize the high Al composition layer.

<Oxidation step of partially oxidizing 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). Conceivable. This oxidation step is an oxidation step using water vapor, and is performed in an atmosphere containing 0.001 to 0.01 g/L of water vapor, preferably 0.008 g/L or less. In order to prevent the water vapor content in the atmosphere around the high Al composition layer 41 from changing significantly during the oxidation process, the high Al composition layer 41 was oxidized with a gas containing 0.001 to 0.01 g/L of water vapor at 10 to 30 L/min. It is more preferable to continue to flow toward As for the gas containing 0.001 to 0.01 g/L of water vapor, it is more preferable that the water vapor is contained in an inert gas such as nitrogen or argon in order to ensure the reproducibility of the oxidation rate.

The inventors speculate that whether the oxidation rate is supply rate-determining or reaction rate-determining 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 variations in the reaction rate due to variations in temperature on the oxidation rate is reduced. On the other hand, when the concentration of water vapor exceeds 0.01 g/L, the supply is sufficient and the oxidation rate becomes reaction rate-determining. . Under the supply rate-determining conditions, it is expected that the effect of crystal anisotropy (the effect of different reaction rates depending on the crystal orientation) is also reduced. 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, making the production process impractical. /L.

The temperature at which the oxidation treatment is performed (stage temperature) is suitably a temperature higher than the conventionally considered appropriate temperature, which is 480 to 580°C, preferably 510 to 580°C. Since it is difficult to strictly measure the surface temperature of the semiconductor stack during the oxidation process, the stage temperature (set temperature) immediately before the oxidation process after mounting the wafer is the oxidation process temperature. do. If the stage temperature is less than 480° C., the oxidation rate is too low and the time required for the oxidation process is too long at the above water vapor concentration, which is not practical as a manufacturing process. On the other hand, if the stage temperature exceeds 580° C., oxidation will occur rapidly, so that semiconductor layers other than the high Al composition layer, which is not intended to be oxidized, will be greatly affected, and adverse effects such as roughening of the surface of the semiconductor laminate may occur. occurs. Moreover, the oxidation time in this step may be appropriately set in accordance with the water vapor concentration and the temperature (stage temperature) at which the oxidation treatment is performed according to the required constriction shape. Although not intended to be limiting, the oxidation time can be, for example, 10 minutes to 3 hours.

FIG. 2 shows a configuration example of a steam oxidation apparatus 100 for performing such an oxidation process. A mechanism 110 for supplying a constant amount of water by a mass flow controller and supplying a constant amount of steam heated to 100 degrees or more (for example, 180 degrees) in a pure water vaporizer, and preheating the steam (for example, 120 degrees ) A mechanism 120 for transporting the wafer W to the stage using an inert gas such as nitrogen gas, a mechanism (not shown) for transporting and recovering the wafer W onto the stage, and a mechanism 130 for heating the stage to a specific temperature (stage temperature). and have Furthermore, in order to reliably stop the oxidation of the high Al composition layer during the oxidation time from when the supply of the gas containing water vapor to the wafer on the stage is started until when the supply is stopped, the gas containing water vapor is stopped. It may also have a mechanism 140 for spraying the wafer with a gas that does not contain water vapor. FIG. 2 also shows an exhaust port 150 for exhausting the gas introduced into the chamber.

Semiconductor elements can be obtained by dicing the epitaxial wafer obtained through the above steps. Prior to dicing, as shown in step D in FIG. be. Moreover, the form of the electrodes is not limited to this example, and may be appropriately provided according to the form of the semiconductor element.

<Epitaxial wafer>
Reference is made to the reference numerals in FIG. The epitaxial wafer obtained by the above 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 constriction layer 40 is formed by the oxidized regions 42 sandwiching the high Al composition layer 41 and the high Al composition layer 41 in the same plane. This epitaxial wafer has a mesa structure in which the side surface of the current confinement layer 40 is exposed, and variations in the amount of oxidation of the current confinement layer 40 within the wafer surface can be suppressed. Here, suppression of variations in the amount of oxidation within the wafer surface means that 19 or more measurement points within the wafer surface of the non-oxidized constriction region of the current confinement layer 40 are measured to form constriction-shaped crystals. When the width of the <01-1> orientation and the width of the <010> crystal orientation are measured, 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.

Regarding the crystal orientation of a zincblende semiconductor crystal with the (100) plane as the upper surface, when the orientation flat (OF) of the substrate used is the (011) plane, the crystal orientation <01-1> is the OF horizontal. The crystal orientation <010> corresponds to a direction oblique to OF at 45 degrees.

<Method for measuring non-oxidized region (constriction shape) of current confinement layer>
The 19 or more measurement points within the wafer plane have 19 positions (P ₁ to P ₁₉ ) shown in FIG. 3 including the center P ₁ within the wafer plane. When measuring more than 19 points, a position not overlapping with the 19 points shown in FIG. 3 shall be selected as the measurement point. The positions of measurement points P ₁ to P ₁₉ are determined as follows.

First, let the center of the wafer be point _P1 . On a straight line parallel to OF and passing through point _P1 , two points within a distance _L1 from the wafer edge are defined as points _P2 and _P3, respectively. Next, _{P 4 ,} P ₅ , . . . P ₁₅ . Further, the vertices of each side of a square having sides parallel to OF and having a side length of L ₃ are defined clockwise as P ₁₆ , P ₁₇ , P ₁₈ and P ₁₉ . The distances L ₁ , L ₂ and L ₃ are 5/76, 11/20 and 11/64 of the wafer diameter, respectively.

As a method for measuring the constricted shape, taking advantage of the fact that the transmittance changes due to oxidation, the constricted shape may be photographed from a bird's-eye view using, for example, an infrared camera. Observing the photographed image, the size of the non-oxidized region (constriction shape) of the current confinement layer can be measured from the contrast difference between the oxidized region and the non-oxidized region.

<Regarding the shape of the non-oxidized region (constriction shape) of the current confinement layer>
As with the mesa structure, the non-oxidized region (constriction shape) of the current confinement layer may have a circular shape, a polygonal shape such as a quadrangle or a hexagon, or a rectangular shape when the semiconductor laminate is viewed from above. You can change the aspect ratio like

<Regarding suppression of anisotropy>
According to the manufacturing method of the present invention, the shape accuracy of the non-oxidized region (constriction shape) of the current confinement layer 40, 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 made of AlxGa1-xAs (0.9≤x<1) is formed, the constriction shape is also circular. The average ratio of the width of the <010> crystal orientation (diameter of the constricted shape) to the width of the <01-1> crystal orientation (diameter of the constricted shape) in the circle is 100 to 102%, which is higher than in the past. Can be precision. It is preferable that both the mesa structure and the constricted shape are circles with no distortion, because the current spreads easily and the efficiency as a semiconductor element can be increased. In the following examples, the diameter of the narrowed shape is also referred to as the narrowed diameter.

EXAMPLES Next, the present invention will be described in more detail using examples, but the present invention is not limited to the following examples.

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

Next, a resist was applied to the upper surface of the upper reflective layer, and a resist mask was formed by photolithography in which circles with a diameter of 50 μm were arranged in a pattern arranged vertically and horizontally at intervals of 220 μm. After that, a dry etching apparatus was used to etch the region not masked by the resist mask until a part of the lower reflective layer was exposed from the upper reflective layer. As a result, a mesa structure in which parts of the upper reflective layer, the high Al composition layer, the light emitting layer, and the lower reflective layer are arranged in a cylindrical shape in a specific pattern was produced, and 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 apparatus. In the oxidation treatment, the layer having a high Al composition ratio (corresponding to the high Al composition layer, the lower reflective layer, and part of the upper reflective layer in Example 1) was slid from the side wall of the cylinder toward the center of the cylinder. be oxidized. In the steam oxidation apparatus, 180° C. steam produced in a pure water vaporizer is mixed with 120° C. nitrogen gas, and the mesa structure of the wafer mounted on the stage heated to 540° C. in the processing chamber is treated. sprayed. At this time, the pressure of the processing chamber was set to normal pressure, and the steam concentration of the sprayed gas was adjusted to 0.005 g/min by adjusting the steam flow rate to 0.1 g/min and the gas flow rate of nitrogen gas to 20 L/min. L, and the water vapor content in the atmosphere around the high Al composition layer was set to 0.005 g/L. The time for the oxidation treatment was set to 110 minutes, and the supply of the gas containing water vapor was stopped, and the oxidation treatment was stopped by blowing nitrogen gas at 25° C. onto the mesa structure of the wafer.

Subsequently, the amount of oxidation of the wafer after the oxidation treatment was measured. Using an infrared camera, the mesa diameter (peripheral diameter) and the diameter of the non-oxidized region were measured at 19 locations within the wafer surface from the upper reflective layer side (positions shown in FIG. 3 described above with OF facing downward). (constriction diameter) were measured respectively.

Since the resist mask is circular, the mesa shape formed by dry etching is circular, and the mesa diameter corresponds to the circular diameter. Therefore, the diameter of the mesa was measured using the orientation flat (011 plane) of the substrate and the diameter in the horizontal direction as a representative value. Regarding the constriction diameter due to oxidation, not only the diameter in the <01-1> direction (horizontal constriction diameter), which is horizontal to the orientation flat, but also the diameter in the <010> direction, which is oblique to the orientation flat at 45° (diagonal constriction diameter). diameter) was also measured.
The constriction diameter was observed using an infrared camera (C9597-42U manufactured by Hamamatsu Photonics). Due to the difference in contrast between the oxidized and non-oxidized regions, the diameter (constriction diameter) was measured by the built-in two-point distance measurement function. Of the infrared camera photographs taken when measuring the stenosis diameter, photographs of points _P16 and _P4 are shown in the figure as representative examples. The dark-colored area in the center of each photograph is the non-oxidized area, and the light-colored area surrounding the dark-colored area is the oxidized area.

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

[Example 3]
The procedure was the same as in Example 1, except that the oxidation treatment was performed for 40 minutes.

[Comparative Example 1]
In the oxidation treatment, by adjusting the flow rate of water vapor to 1.2 g/min and the gas flow rate of nitrogen gas to 20 L/min, the water vapor concentration of the sprayed gas is set to 0.06 g/L per minute, and the atmosphere around the high Al composition layer Example 1 was repeated except that the water vapor content was 0.06 g/L, the stage temperature was 520° C., and the oxidation treatment time was 29 minutes and 40 seconds (29.7 minutes). Among the infrared camera photographs taken when measuring the constriction diameter, photographs of points _P16 and _P4 are shown in the figure as representative examples.

[Comparative Example 2]
In the oxidation treatment, by adjusting the flow rate of water vapor to 1.2 g/min and the gas flow rate of nitrogen gas to 20 L/min, the water vapor concentration of the sprayed gas is set to 0.06 g/L per minute, and the atmosphere around the high Al composition layer The same procedure as in Example 1 was carried out, 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 flow rate of water vapor to 0.4 g/min and the gas flow rate of nitrogen gas to 20 L/min, the water vapor concentration of the sprayed gas is set to 0.02 g/L per minute, and the atmosphere around the high Al composition layer The same procedure as in Example 1 was carried out, 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 constriction diameter due to oxidation in the oxidation treatments according to Examples 1 to 3 and Comparative Examples 1 to 3. Note that the horizontal constriction diameter (μm) and diagonal constriction diameter (μm) in the table indicate the average value and standard deviation (σ) of the 19 points shown in FIG. is described in Table 1 as "oblique/horizontal" (%).

From the results in Table 1, although the oxidation treatment time is longer in Examples 1 to 3 than in Comparative Examples 1 to 3, the standard deviation (.sigma.), which indicates the variation in constriction diameter, is small. Therefore, in Examples 1 to 3, it was found that variation in the amount of oxidation within the wafer surface can be suppressed. In addition, since the ratio of oblique/horizontal is close to 100%, it was found that the mesa shape can be oxidized more isotropically (while suppressing the influence of anisotropy).

(Evaluation 1: Evaluation of difference in oxidation rate depending on Al composition)
In Example 1 and Comparative Example 1 described above, the current confinement layer was formed by oxidizing the Al _0.963 Ga _0.037 As after crystal growth to 30 nm. Instead, a sample in which the current confinement layer was formed from Al _0.976 Ga _0.024 As and a sample in which the current _confinement layer was formed from AlAs were prepared. The oxidation rate (=(mesa diameter−constriction diameter)/2/processing time) was measured depending on the difference in the Al composition of the current confinement layer. FIG. 5 shows the results of the oxidation treatment at 520° C. with a water vapor concentration of 0.06 g/L·min, and FIG. 6 shows the results of the oxidation treatment at 540° C. with a water vapor concentration of 0.005 g/L·min.

From the graphs of FIGS. 5 and 6, it was found that the oxidation treatment according to this manufacturing method can slightly reduce the change in the oxidation rate due to the difference in Al composition. This may lead to the suppression of variations in constriction diameter in Table 1.

(Evaluation 2: Evaluation of forward voltage)
A metal layer made of Au/Zn was vapor-deposited on the upper reflecting layer of the oxidized wafer, and annealed at 460° C. to form an upper electrode. After that, a metal layer composed of Au/Ni/Ge was vapor-deposited on the rear surface of the GaAs substrate to form a rear surface electrode, which was then annealed at 410° C. to form a rear surface electrode.

A dicer was used to cut the part where the lower reflective layer of the mesa structure was partly exposed, and the product was divided into individual surface-emitting laser chips. The chips were mounted on metal stems with silver paste and wire bonded to the top electrodes with gold wires.

Using a constant-current voltage measuring device, the forward voltage when a current of 10 mA was applied was measured at 10 points (horizontal direction of the orientation flat) at equal intervals in the radial direction from the center of the wafer to the outer circumference of the wafer within the wafer surface. The measurement results in Comparative Example 1, Comparative Example 3, and Example 1 are shown in FIG.

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

According to the present invention, it is possible to provide a large amount of semiconductor devices, such as surface emitting lasers, of which the variation in the amount of oxidation within the wafer surface is suppressed, the variation in constriction shape is small, and the quality is stable.

REFERENCE SIGNS LIST 1 semiconductor element 10 substrate 20 lower reflective layer 30 light emitting layer 40 current constriction layer 41 high Al composition layer 42 oxidized region 50 upper reflective layer 100 steam oxidation device

Claims (2)

Having 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 is provided on the outer peripheral side of the mesa structure and sandwiched between oxidized regions in the same plane as the high Al composition layer to constitute a current constriction layer;
When 19 or more constricted shapes in the wafer surface are measured by overlooking the constricted region that is not oxidized, the width of the crystal orientation <01-1> and the width of the crystal orientation <010> of the constricted shape are standardized. All the deviations are 0.6 μm or less,
An epitaxial wafer, wherein an average ratio of the width of the crystal orientation <010> to the width of the crystal orientation <01-1> is 100 to 102%. 2. The epitaxial wafer of claim 1, wherein said constriction shape is circular.

Images