JPH08167584A - Manufacture of epitaxial wafer - Google Patents

Abstract

PURPOSE: To efficiently remove surface defects in the periphery of an epitaxial wafer by a method wherein an epitaxial layer is grown on a semiconductor substrate, and the surface of the epitaxial layer is flattened by grinding. CONSTITUTION: An N-type GaP epitaxial layer 12 and a Zn-O doped P-type GaP epitaxial layer 13 are successively grown on an N-type GaP single crystal substrate 11 through a liquid epitaxial growth method to obtain a GaP epitaxial wafer 10 used for a red light emitting element. As the surface of the GaP epitaxial wafer 10 used for a red light emitting element is curved like a concave just after the Zn-O doped P-type GaP epitaxial layer 13 is grown, the curved surface of the GaP epitaxial wafer 10 is accurately flattened into a flat plane by a surface grinder. By this setup, surface defects produced in the peripheral part of the GaP epitaxial wafer 10 used for a red light emitting element are capable of being efficiently removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an epitaxial wafer for manufacturing a light emitting device. More specifically, it relates to a method for flattening the surface of an epitaxial wafer having an epitaxial layer grown on a semiconductor substrate.

[0002]

BACKGROUND OF THE INVENTION A light emitting device such as a light emitting diode is usually manufactured by growing a plurality of epitaxial layers on a substrate (wafer) made of a compound semiconductor and converting the epitaxial layers into devices.

Generally, the surface of an epitaxial wafer (epitaxial layer) is not flat, and especially when it is grown by a liquid phase epitaxial growth method, the outer peripheral portion of the wafer becomes thick, and the thickness variation in the wafer surface is large, and it is difficult to use as it is. . Further, surface defects are likely to occur on the outer peripheral portion of the wafer. Therefore, conventionally, the surface of an epitaxial wafer has been subjected to surface polishing using a polishing liquid (colloidal silica) containing abrasive grains such as silica particles to planarize and remove surface defects.

[0004]

However, in the mechanochemical polishing such as the surface polishing using the conventional polishing liquid, the surface defects on the outer peripheral portion of the wafer cannot be sufficiently removed. This is, for example, oxygen-doped GaP
In the case of an epitaxial layer, Ga ₂ O ₃ is formed around the wafer.
Precipitates are generated to form defects, but in order to remove them, it is necessary to polish by 30 μm or more, but if they are polished too much, a relatively thin region in the center of the wafer will be polished more than necessary. Is.

Therefore, the surface defects on the outer peripheral portion of the wafer which cannot be removed by the surface polishing are removed by partially cutting the wafer only at the defective portion or by cutting (chamfering) the outer peripheral portion with a constant width. However, in this method, many portions are removed, which causes a decrease in yield.

It is an object of the present invention to provide a method for efficiently removing surface defects generated in the outer peripheral portion of an epitaxial wafer and reducing variations in thickness within the wafer surface.

[0007]

The present invention includes a step of growing an epitaxial layer on a semiconductor substrate and then grinding and flattening the surface of the epitaxial layer.

The epitaxial layer is formed by, for example, a liquid phase epitaxial growth method.

The semiconductor substrate and the epitaxial layer are made of, for example, a III-V group compound semiconductor, and more specifically, a compound semiconductor selected from, for example, GaP, GaAs, and GaAlAs.

In the grinding process, it is desirable that the thickness variation defined by the difference between the maximum thickness and the minimum thickness in the plane of the epitaxial wafer is 5 μm or less.

[0011]

[Function] Epitaxial wafer (epitaxial layer)
The surface of the wafer is flattened mechanically and highly accurately by grinding the surface of the wafer into a planar shape by a surface grinding device or the like. In this case, the outer peripheral portion of the wafer which is curved and protrudes in a concave shape is deeply ground, while the relatively thin region in the central portion of the wafer is shallowly ground. Therefore, it is possible to efficiently remove the thick peripheral region with many surface defects without grinding the central portion more than necessary, and reduce the variation in the thickness within the wafer surface.

[0012]

EXAMPLES Next, examples of the present invention will be described in detail.

FIG. 1 is a conceptual diagram of the method of the present invention. That is, as shown in FIG. 1A, the surface of the epitaxial wafer 1 immediately after the epitaxial layer 3 is grown on the semiconductor substrate 2 by the liquid phase epitaxial growth method is concavely curved. As shown in FIG. 1B, this curved surface is highly precisely ground into a flat surface by using a surface grinder. Hereinafter, the evaluation results of the epitaxial wafers of Examples and Comparative Examples will be specifically described.

(Example) An n-type GaP epitaxial layer 12 and Z were formed on an n-type GaP single crystal substrate 11 having a diameter of about 48 mm.
The n-O-doped p-type GaP epitaxial layer 13 was sequentially grown by a liquid phase epitaxial growth method to obtain a GaP epitaxial wafer 10 for a red light emitting device having a thickness distribution as shown in FIG. 2 (a).

This epitaxial wafer 10 was ground under the following grinding conditions using a fully automatic grinding machine SVG-201 manufactured by Shibayama Kikai Co., Ltd. as a surface grinder, and the epitaxial wafer shown in FIG. 20 (target thickness 295 μm) was obtained. Grinding wheel: Resin bond # 2000 type F Table rotation speed: 100 rpm Spindle rotation speed: 2400 rpm Grinding wheel feed speed: 20 to 30 μm / min

The variation in thickness of the epitaxial wafer 20 (the number of samples: 500) which has been subjected to the above-mentioned grinding processing was evaluated, and the results are shown in Table 1. Specifically, the thickness is measured at 9 points on the wafer surface (4 points at 3 mm from the outer circumference, 4 points at the radius r / 2 from the outer circumference and 1 point at the center), and the maximum thickness and the minimum thickness are measured. The difference was defined as the variation R (μm).
It should be noted that a number with an underline indicates that the number is included, and a number without an underline indicates that the number is not included.

Next, the epitaxial wafer 20 is formed into a light emitting diode, and a V _F value (forward operation current,
For example, the applied voltage required to pass 10 mA) and the brightness were measured. That is, as shown in FIG. 3A, the epitaxial wafer 20 that has been subjected to the grinding process is processed into the p-side electrode 14 (100 μmφ, 350 μm) corresponding to each individual element.
m pitch) and n-side electrode 15 (50 μmφ, 100 μm
Pitch), and half dicing is performed for each individual element to form the separation groove 17, and about 1400 per wafer is formed.
0 mesa type light emitting diodes 16 (300 μm × 300
(FIG. 3 (b)), and then dicing strain removing etching (hydrochloric acid, 80 ° C., 15 minutes) was performed.

The V _F value and the luminance of the thus obtained mesa type light emitting diode 16 were measured at a frequency of one every four in the vertical and horizontal directions, and the entire surface of the wafer was mapped. 4 and 5 show the frequency distribution of the V _F value and the luminance of the sample, respectively.

[0019]

[Table 1]

(Comparative Example) The same type of epitaxial wafer 10 as that used in the example was polished to the same target thickness as that of the example using a polishing liquid containing colloidal silica. The variation in the thickness of the epitaxial wafer 20 (the number of samples: 500) subjected to this treatment was evaluated, and the results are shown in Table 1 together with the examples. Further, this epitaxial wafer 20 was formed into a light emitting diode as in the example, and the V _F value and the brightness were measured. The result is shown in Figure 4.
5 and FIG. 5 together with the examples.

(Evaluation result of thickness variation) As can be seen from Table 1, the thickness variation R by polishing in the comparative example is 10 to 15 μm, which is the largest at 46.8%, and the average value is 12.6 μm. In comparison with the comparatively large value, the thickness variation R due to the grinding process of the example is 100% in 0 to 5 μm.
It was confirmed that the wafers were concentrated and the average value was 2.5 μm, which was extremely small, and a wafer having a uniform thickness was obtained. Further, the process yield was 77.8% in the comparative example, whereas it was 93.4% in the example, which was also a good result.

(Evaluation result of device characteristics) As can be seen from the respective drawings, according to the method of the embodiment, both the V _F value and the luminance are extremely smaller than those of the comparative example, and good results are obtained. In addition, in the case of the example, both the wavelength characteristics and the appearance inspection were at a level without problems.

[0023]

As described above, according to the present invention, it is possible to efficiently remove the surface defects that often occur in the outer peripheral portion of the epitaxial wafer that is curved and convex in a concave shape, which contributes to the improvement of the yield and to the epitaxial growth. Enables standardization of wafers. Further, since the wafer surface can be accurately flattened, it is possible to supply a wafer having a small variation in thickness. Therefore, the surface inspection and thickness measurement of the epitaxial wafer can be simplified.

From the aspect of using an epitaxial wafer, there is an advantage that yield and productivity can be improved or product uniformity can be obtained. Specifically, since the wafer surface is accurately flattened, electrodes can be formed in a predetermined shape and size. Further, since the surface defects on the wafer surface are efficiently removed, the number of defective elements due to the surface defects can be reduced. Further, since the thickness of the epitaxial wafer is controlled uniformly, the device characteristics can be made uniform, and the chip thickness (height) becomes uniform, which can reduce process troubles during the assembly process. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a method of processing a surface of an epitaxial wafer according to the method of the present invention.

FIG. 2 is an explanatory view showing a surface processing method of an epitaxial wafer according to the method of the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a method of processing a GaP epitaxial wafer for a red light emitting device into a mesa type light emitting diode.

FIG. 4 is a graph showing V _F value distributions of the mesa type light emitting diodes obtained in Examples and Comparative Examples.

FIG. 5 is a graph showing a relative luminance distribution of the mesa type light emitting diodes obtained in Examples and Comparative Examples.

[Explanation of symbols]

 1, 10 20 Epitaxial wafer 2 Semiconductor substrate 3 Epitaxial layer 11 n-type GaP single crystal substrate 12 n-type GaP epitaxial layer 13 Zn-O-doped p-type GaP epitaxial layer 14 p-side electrode 15 n-side electrode 16 Mesa-type light-emitting diode 17 Separation groove

Claims (5)

[Claims] 1. A method for manufacturing an epitaxial wafer, which comprises a step of growing an epitaxial layer on a semiconductor substrate and then grinding and flattening the surface of the epitaxial layer. 2. The method of forming the epitaxial layer is a liquid phase epitaxial growth method.
A method for manufacturing an epitaxial wafer according to item 1. 3. The method for producing an epitaxial wafer according to claim 1, wherein the semiconductor substrate and the epitaxial layer are made of a III-V group compound semiconductor. 4. The group III-V compound semiconductor is Ga.
The epitaxial wafer manufacturing method according to claim 3, wherein the epitaxial wafer is selected from P, GaAs, and GaAlAs. 5. The thickness variation defined by the difference between the maximum thickness and the minimum thickness within the epitaxial wafer surface in the grinding process is 5 μm or less, and the grinding process according to claim 1 or 2. Method of manufacturing epitaxial wafer.