JPH07330485A - Apparatus for production of multilayered epitaxially grown crystal - Google Patents

Abstract

PURPOSE:To obtain epitaxial wafers adequate as light emitting diodes by growing thick epitaxial layers having less changes in mixed crystal ratios with respect to a growth direction. CONSTITUTION:The apparatus for growing, in liquid phase, the multielement mixed crystal epitaxial layers on plural sheets of the wafers by a slow cooling method has a substrate holder 5 which is provided with a housing section 6 and a wafer holder 1 which holds the plural wafers 2, 3 and is installed in the housing section 6. Spacings 7, 8 exist between the wafers 2, 3 and the housing section 1. The melt volume is >=1.5 times the product of the total area of the wafers 2, 3 and the melt thickness. Al and As are supplied at the growth boundary by the convection from the spacings 7, 8 in addition to the diffusion transportation occurring in a concn. gradient and, therefore, the change in the mixed crystal ratios with respect to the growth direction is suppressed. The thick and uniform epitaxial layers are thus formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a multi-element mixed crystal multilayer epitaxial growth crystal used for semiconductor materials and the like.

[0002]

2. Description of the Related Art Multi-wafer type multi-layer epitaxial growth crystals are industrially manufactured by performing epitaxial growth at the interface between a substrate crystal attached to a wafer holder and a melt. Specifically, as shown in FIG. 1, a plurality of wafers 2, 3 ... Are attached to both sides of the wafer holders 1, 1 ,. The melt 4 is brought into contact. The size of the melt 4 facing the wafers 2, 3 ... Is set to be substantially the same as that of the wafers 2, 3 ... and the thickness is usually set to about 2 mm. Under these conditions, an epitaxial layer is grown from the melt 4 on the wafers 2, 3 ... While gradually cooling. The obtained epitaxially grown crystal is manufactured as an epitaxial wafer for a GaAlAs light emitting diode having a single heterojunction.

[0003]

By the way, GaAlAs-based light-emitting diodes having a single heterojunction are
Since the p-type GaAlAs epitaxial layer and the n-type GaAlAs epitaxial layer are sequentially deposited on the As substrate crystal, the light emission output, which is an important characteristic as a light-emitting diode, greatly affects the thickness of the n-type epitaxial layer. To be done. Further, in order to obtain a sufficient light emission output, an extremely thick epitaxial layer of 40 to 45 μm is required. Furthermore, the n-type GaAlAs layer needs to have a high AlAs mixed crystal ratio so that a sufficient hetero barrier can be obtained and that there is no absorption for the wavelength of emitted light. On the other hand, in the conventional slow cooling method, it is difficult to secure a sufficient melt thickness due to space restrictions. Therefore, as compared with a single-wafer type epitaxial growth apparatus in which a sufficient melt thickness is secured, it is unavoidable that the thickness of the obtained epitaxial layer becomes thin, and a light emitting diode having sufficient light emitting characteristics cannot be obtained.

In the epitaxial layer obtained by the usual slow cooling method, the mixed crystal ratio distribution in the thickness direction decreases from the start of growth toward the surface as shown in FIG. That is, the mixed crystal ratio changes in the thickness direction in the epitaxial layer, and the mixed crystal ratio decreases near the surface. As a result, absorption of the emitted light wavelength is observed. The present invention has been devised to solve such a problem, and by using a wafer holder having a shape in which the melt injected into a gap other than the wafer holding portion is convected to the wafer holding portion, it is thick and mixed. The purpose of the present invention is to grow an epitaxial layer suitable for a light emitting diode having no reduction in crystal ratio on a substrate crystal.

[0005]

In order to achieve the object, a manufacturing apparatus of the present invention is an apparatus for liquid phase growing a multi-component mixed crystal epitaxial layer on a plurality of wafers by a slow cooling method, and a substrate provided with a containing section. A holder and a wafer holder that holds a plurality of wafers and is installed in the accommodating unit, and the accommodating unit and the wafer so that the melt volume is 1.5 times or more the product of the total area of the wafer and the melt thickness. It is characterized in that a gap is formed between and. The wafer holder may have a shape similar to or different from the wafer shape.

[0006]

In the conventional slow cooling method of liquid phase epitaxial growth, supersaturated As produced by slow cooling is diffused and transported in the melt having a size almost the same as the wafer shape by the concentration gradient at the interface with the substrate crystal, and To grow epitaxially. At this time, the composition of the melt is set in a state of equilibrium with the mixed crystal ratio of the solid phase at the growth temperature,
Particularly, the higher the solid phase AlAs mixed crystal ratio, the lower the As concentration in the equilibrated melt. Therefore, it is very difficult to obtain a thick growth layer with an epitaxial layer having a high AlAs mixed crystal ratio. Furthermore, in a liquid phase epitaxial device in which simultaneous growth is performed on a plurality of substrate crystals, spatial restrictions become stricter as the number of substrate crystals used increases.
It becomes difficult to secure a sufficient amount of melt. Therefore, high Al
It becomes more difficult to obtain a thick growth layer from an epitaxial layer having an As mixed crystal ratio. Moreover, since the segregation coefficient of Al changes with temperature, the mixed crystal ratio of the epitaxial layer obtained by liquid phase epitaxial growth by the slow cooling method changes in the thickness direction.

The present invention has been completed on the premise of recognizing the problem in such a conventional slow cooling method, and transports As to the growth interface by the convection melt in the wafer holding part, so that the epitaxial film thicker than the normal growth film thickness is obtained. It is to grow a layer. That is, in a liquid-phase epitaxial device for performing epitaxial growth on a plurality of wafers at the same time, a wafer holder having a gap other than the wafer holder is used. The melt injected into the gaps convects to the wafer holding portion at any time and transports As to the growth interface.
In this method, supersaturated As generated by slow cooling is not only diffused and transported according to the concentration gradient at the interface with the substrate, but is also transported by convection from a gap other than the wafer holding portion. As a result, it becomes possible to obtain an epitaxial layer thicker than the normal grown film thickness. Further, As and Al are consumed in the wafer holding portion, but As and Al are consumed by the convection of the melt in the gaps other than the wafer holding portion.
Since Al and Al are transported to the growth interface, the change in the mixed crystal ratio in the growth direction of the epitaxial layer is smaller than that in the conventional method.

For example, as shown in FIGS. 2 and 3, the accommodating portion 6 of the substrate holder 5 may have a two-step bottom, and a gap 7 may be provided between the bottom surface and the step. Alternatively, the gap 8 may be provided in the upper part of the housing 6 by making the housing 6 deep. Due to the gaps 7 and 8, the volume of the melt 4 accommodated is larger than that in the case where the conventional wafer holder is used. In order to obtain the action and effect of the gaps 7 and 8, the gaps 7 and 8 are set so that the melt volume becomes 1.5 times or more as compared with the product of the total area of the wafers 2, 3 ... And the thickness of the melt 4. It is necessary to provide. The epitaxial layer grown under such conditions is thick and the change in the mixed crystal ratio is suppressed. Therefore, the light emitting diode manufactured from the obtained epitaxial wafer becomes a product exhibiting excellent light emitting characteristics.

[0009]

EXAMPLE In this example, as shown in FIG. 2, GaAs crystal substrates 2 and 3 each having a diameter of 3 inches were attached to both sides of a wafer holder 1 and placed in an accommodating portion 6 of a substrate holder 5 shown in FIG. . As growth materials, Ga, Al, and As that are saturated and dissolved at 910 ° C. were prepared in a growth melt holder (not shown). A waste liquid holder (not shown) was attached to the bottom of the substrate holder 5. The substrate holder 5 has a deeper accommodation portion 6 than the conventional holder, and gaps 8 and 7 are formed between the inner surface of the accommodation portion 4 and the wafers 2 and 3. Therefore, the volume of the melt 4 stored in the storage portion 6 was 1.5 times the product of the total area of the wafers 2 and 3 and the melt thickness. The melt 4 injected into the gaps 8 and 7 convects in the housing 6 in accordance with the temperature gradient generated in the housing 6, and passes between the crystal substrates 2 and 3.

After keeping the whole at 910 ° C. in a hydrogen atmosphere, the growth raw material was poured from the growth melt holder into the accommodating portion 6 of the substrate holder 5, and the whole was gradually cooled to 870 ° C. In the process of slow cooling, GaA is deposited on the crystal substrates 2, 3 ...
The lAs epitaxial layer was grown and an epitaxial wafer was manufactured. The thickness distribution of the obtained epitaxial layer is shown in FIG. 5 in comparison with the result obtained by the conventional method. As is apparent from FIG. 5, the epitaxial layer grown according to the present invention is thicker and more uniform than the conventional method. Further, as is clear from FIG. 4 in which the mixed crystal ratio distribution in the epitaxial layer is compared with the conventional method, it can be seen that the change in the mixed crystal ratio in the growth direction is significantly smaller than that in the conventional method. From these results, it was confirmed that the obtained epitaxial wafer was used as a material for a light emitting diode exhibiting excellent light emitting characteristics.

[0011]

As described above, according to the present invention, a wafer holder having a gap other than the wafer holding portion is used, and the melt injected into the gap is positively convected to the growth interface, whereby the growth is performed. In addition to As diffusion transport due to the concentration gradient near the interface, As and Al are sent to the growth interface by convection transport. Therefore, the influence of As consumed as the epitaxial layer grows is suppressed, and a thick and uniform epitaxial layer is formed. As a result, a GaAlAs-based light emitting diode epitaxial wafer having a single heterojunction exhibiting excellent light emitting characteristics can be obtained.

[Brief description of drawings]

FIG. 1 Wafer accommodating part of an epitaxial crystal growth apparatus by a conventional method

FIG. 2 is a view illustrating a wafer accommodating portion according to an embodiment of the present invention.

FIG. 3 is a substrate holder used in an embodiment of the present invention.

FIG. 4 is a graph comparing the method of the present invention with the method of the related art regarding the mixed crystal ratio distribution in the growth direction of the epitaxial layer.

FIG. 5 is a graph comparing the thickness distributions of epitaxial layers obtained by the method of the present invention and the conventional method.

[Explanation of symbols]

1: Wafer holder 2, 3: Wafer 4: Melt 5: Substrate holder 6: Storage part 7, 8:
Gap

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Seiji Yamashita 3-5-3 Akebonocho, Tachikawa-shi Nisshin Steel Co., Ltd. Semiconductor Research Center (72) Inventor Atsushi Kajimoto 3-5-3 Akebonocho, Tachikawa-shi Nisshin Steel Co., Ltd. Semiconductor Research Center (72) Inventor Shigehiko Nomura 3-5-3 Akebonocho, Tachikawa City Nisshin Steel Co., Ltd. Semiconductor Research Center

Claims (1)

[Claims] 1. An apparatus for performing liquid phase growth of a multi-element mixed crystal epitaxial layer on a plurality of wafers by a slow cooling method, a substrate holder having a housing, and a wafer holder for holding the plurality of wafers and installed in the housing. And the melt volume is 1.5 times the product of the total area of the wafer and the melt thickness.
A manufacturing apparatus for a multilayer epitaxial growth crystal, characterized in that a gap is formed between the accommodation portion and the wafer so as to be more than double.