JP3427466B2 - Manufacturing method of semiconductor epitaxial wafer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface treatment of compound semiconductor epitaxial wafers.

[0002]

2. Description of the Related Art Compound III-V compound semiconductors such as gallium arsenide (hereinafter referred to as GaAs) and aluminum gallium arsenide (hereinafter referred to as AlGaAs), which are compound semiconductors, have a direct transition type bandgap, so that a light emitting diode (hereinafter referred to as LED)
It is used as a light-emitting element such as. Silicon (hereinafter referred to as Si) -doped GaAs or AlGaAs epitaxial wafers are widely used for infrared emitting LEDs.
The Si dopant that creates a deep level is generally 5 × 10 5.
^{Doped at} a high concentration of ¹⁸ cm ^-3 or more. S in the crystal
Since the i concentration is high, the deep level concentration is also high.
The light emission output when ED is high. Such a wafer is grown by a liquid phase epitaxial method (hereinafter referred to as LPE). In this method, for example, when growing a GaAs layer on a GaAs substrate, a Ga solution in which Si and arsenic (hereinafter referred to as “As”) are dissolved in a hydrogen atmosphere at about 900 ° C.
Contact the GaAs substrate at a high temperature. In general, the As concentration of the Ga solution is made slightly unsaturated, and the GaA
s The substrate surface is melted by 10 to 20 μm. This is called a meltback process, and the crystal defects due to damage during processing of the GaAs surface, and the surface where As is missing to raise the temperature to about 900 ° C. are removed by this. After this meltback, a GaAs layer is grown on the surface of the GaAs substrate while being gradually cooled. In the grown GaAs layer, Si dopant is G
It is taken into the aAs layer crystal. However, when the GaAs layer grows below 700 ° C, the solubility drops sharply,
At about 650 ° C., the dissolved concentration of As usually disappears, so the GaAs layer grows only slightly below 650 ° C.

[0003]

On the other hand, since the solubility of Si is large even at 650 ° C., further slow cooling causes the Si in the Ga solution to become supersaturated, and Si often precipitates on the surface of the GaAs layer, for example, 60 to 70 μm. In some cases, about 700 Si crystals / cm ² were deposited on the surface of the GaAs epilayer. This Si precipitate has a pyramid shape and sometimes has a size of several mm, which is an obstacle to the subsequent steps. For example, if Si is deposited when an electrode is attached to the surface of a GaAs layer for LED processing, LED processing cannot be performed because Si precipitates are present on the epilayer surface. Therefore, in order to remove the Si precipitate, conventionally, the surface of the GaAs layer with the Si precipitate is first mechanically removed by lapping, and then the epi surface is mirror-finished by chemical polishing. The drawback of this method is that the surface of the epi layer just before the end of epi growth has a high carrier concentration, so it is easy to make ohmic contact with the electrode.
When the Si precipitates are removed by the above-mentioned method, the portion having a high carrier concentration is also removed, so that it becomes difficult to make ohmic contact. On the other hand, the Ga on the surface of the epi-layer is
As an etching solution for removing Si without removing the surface layer of the As layer, an alkaline aqueous solution described in JP-A-5-182949 such as KOH is known.
The selective etching property of Si is by no means sufficient, and
Si deposited basically in the form of a single crystal could hardly be removed. Therefore, a method for selectively removing Si precipitates has been desired.

[0004]

Therefore, the inventors of the present invention utilize the difference in the solubility temperature dependence of GaAs and Si in a Ga solution to form Si on the surface of a Si-doped GaAs layer on which Si precipitates are present. Saturated Ga solution at 200 ℃ ~ 800
It was found that the Si precipitates can be dissolved without dissolving GaAs by keeping them in contact with each other at ℃,
The present invention has been reached. That is, the object of the present invention is to add S to the surface.
An object of the present invention is to provide a silicon-doped GaAs or AlGaAs epitaxial wafer which is free of i-precipitates and which can easily form an ohmic contact. A method for manufacturing a semiconductor epitaxial wafer, characterized in that, after the growth of the layer doped with silicon, silicon is brought into contact with an unsaturated gallium solution at a temperature of 200 to 800 ° C., the contact temperature is 300 ° C. to 700 ° C., The gallium solution is easily achieved by a manufacturing method in which silicon is unsaturated, and more preferably, a manufacturing method in which the gallium solution is brought into contact with an epitaxial wafer and then a slow cooling step is performed.

The present invention will be described in more detail below. The semiconductor epitaxial wafer that is the subject of the present invention,
This is a liquid-phase grown GaAs or AlGaAs layer doped with silicon by a conventional method. The gallium solution used in the present invention can be used unless Si is in a saturated or supersaturated state, and may be one in which nothing is added, but in order to increase the solubility of Si in particular, the wafer and the gallium solution are kept at 650 to 800 ° C. When contacting with each other, As is preferably saturated so as not to cause As loss.

In the present invention, the contact temperature between the gallium solution and the wafer is 200 to 800 ° C. However, if the solubility of Si is not higher than a certain level, Si will be saturated immediately, so the more preferable lower limit of the contact temperature. Is preferably 300 ° C. or higher. Further, from the viewpoint of preventing As loss, 700 ° C. or less is preferable. As a more preferred embodiment of the present invention, after the wafer and the gallium solution are contacted with each other, the wafer is gradually cooled while being in contact with each other. By gradually cooling while keeping in contact with the wafer, it is possible to prevent As from coming off by exposing the wafer to the gas at a high temperature.

Specifically, as a method of bringing the wafer into contact with the gallium solution, a slide board as shown in FIG. 1 is used, or a piston or the like is used in a sealed box to reduce the volume. Any method can be used, such as by doing so.

[0008]

【Example】

[Example 1] By the slide method boat shown in FIG. 1, a GaAs substrate having a diameter of 50 mm and a thickness of 300 μm was heated at 900 ° C. in an H ₂ atmosphere, and then As and Si were dissolved on the GaAs substrate. The Ga solution was contacted to start the growth. The growth was completed by cooling to room temperature at 1 ° C / min. A Si-doped GaAs layer of about 140 μm was grown. A PN junction was formed by PN inversion in the epitaxial growth layer. After cooling, after taking out, the Ga solution on the surface of the epitaxial wafer was boiled and removed with an HCl solution. Observation of the surface of this epitaxial wafer revealed that deposits of about 80 to 90 μm were formed on the epi surface at about 50.
It was deposited at a density of 0 pieces / cm ² . This wafer is shown in FIG.
The boat of the slide method shown in was charged. Purity 6N
As and Si were not dissolved in 100 g of Ga solution.
After heating to 500 ° C. in an H ₂ atmosphere, a Ga solution was brought into contact with the GaAs epitaxial wafer. As it is 3
After holding for 0 minutes, the Ga solution was removed from the surface with a slide and cooled to room temperature. After reaching room temperature, the Ga solution was removed from the GaAs epitaxial wafer by boiling and washing with an HCl solution. Even with the naked eye, the Si precipitate was completely removed on the surface. The surface of the GaAs epitaxial layer was slightly dissolved in the Ga solution and the surface was slightly roughened, but this was not a problem in practical use. Similarly, the contact temperature of the Ga solution for removing the Si precipitate is set from 200 ° C. to 700
The surface condition was examined by changing the temperature to ℃. It gave similar results. However, when the temperature exceeds 650 ° C., the surface of the epitaxial layer was dissolved in Ga in a large amount, but there was no problem in practical use.

Example 2 A GaAs substrate having a diameter of 50 mm and a thickness of 300 μm was heated to 900 ° C. in a H ₂ atmosphere by a slide method boat shown in FIG. 1 and then Al and As were deposited on the GaAs substrate. Then, a Ga solution containing Si and Si was brought into contact with each other to start growth. The growth was completed by cooling to room temperature at 1 ° C / min. Si of about 150 μm
A doped GaAs layer has grown. A PN junction was formed by PN inversion in the epitaxial growth layer. Ga on the surface of the epitaxial wafer after being taken out after cooling
The solution was washed by boiling with HCl and removed. When the surface of this epitaxial wafer was observed, it was about 50-60.
Si pyramids of μm were deposited on the surface of the GaAs epitaxial growth layer at a density of about 800 / cm ² . When the Al composition was measured by an electron microanalyzer, x = 0.1 at the start of growth of the Al _x Ga _1-x As layer.
5. The composition of x = 0.01 was changed on the epilayer surface.
The boat of the slide method shown in FIG. 1 was charged. As and Si were not dissolved in 100 g of a Ga solution having a purity of 6N. After heating to 500 ° C in H ₂ atmosphere, GaAs
The Ga solution was brought into contact with the epitaxial wafer. The solution was kept for 30 minutes as it was, the Ga solution was removed from the surface with a slide, and cooled to room temperature. After reaching room temperature, the Ga solution was removed from the GaAs epitaxial wafer by boiling and washing with an HCl solution. Even with the naked eye, the Si precipitate was completely removed on the surface. The surface of the GaAs epitaxial layer was slightly dissolved in the Ga solution and slightly roughened, but there was no problem in practical use. Similarly, the contact temperature of the Ga solution for removing the Si precipitate is set from 300 ° C. to 700
It was changed to ℃. It gave similar results. However, when the temperature exceeds 650 ° C., the surface of the epitaxial layer was dissolved in Ga in a large amount, but there was no problem in practical use.

[Embodiment 3] An epitaxial wafer grown by the same method as in Embodiments 1 and 2 was used. As
G of 6N purity that dissolves S to saturation and does not dissolve Si
The solution a was contacted at 500 ° C. Hereinafter, it is the same as that of the first embodiment. At this time, all the precipitates of Si were dissolved and the surface of the epitaxial growth layer was not dissolved by Ga, and the same surface roughness as before the contact with the Ga solution for Si dissolution was obtained. The contact temperature of the Ga solution in which As was dissolved was changed from 200 ° C to 800 ° C. Exactly the same results were obtained within this temperature range.

[Embodiment 4] An epitaxial wafer grown by the same method as in Embodiments 1 and 2 was used. Si
After contacting a 6N Ga solution in which neither As nor As is dissolved at 500 ° C., 1 ° C./min while keeping the Ga solution in contact
Example 1 is the same as Example 1 except that the cooling rate was to room temperature. At this time, all Si precipitates were dissolved. The surface of the epitaxial growth layer was slightly rough because GaAs was dissolved in Ga. When a similar experiment was conducted at 200 ° C. to 700 ° C., when the temperature exceeded 650 ° C., it was within the practically acceptable range, but the surface roughness was slightly increased, but the dislocated portion was 1 μm or less.

[0012]

According to the present invention, Si precipitates deposited after epitaxial growth can be dissolved and removed on the surface of a Si-doped GaAs or AlGaAs epitaxial wafer. Therefore, as compared with the method of removing Si precipitation and the epi surface together by mechanical polishing or the like, the number of steps is smaller and the productivity is improved. Wafer cracks and chips,
It is possible to prevent mechanical damage such as surface damage. The gallium solution for dissolution can be reused 10 times or more. In addition, the boat to be used can be one for liquid phase epitaxial growth or a boat having a simple structure to process many wafers at a time. As a result, this process can be realized at low cost. Since the Si precipitates can be removed without removing the high-concentration Si layer on the epi surface, the contact resistance of the electrodes can be reduced when processing into an LED or the like. Therefore, it can be used as an epitaxial wafer for an LED for high current. In the example, the slide method boat used in the liquid phase epitaxial growth in which the wafer is horizontally arranged is used, but the liquid phase epitaxial growth boat in which the wafer is vertically arranged and the liquid phase epitaxial growth boat in which the wafer is directly immersed in the gallium solution are used. Needless to say, the same effect can be obtained with the configuration of the present invention regardless of the shape of the container used, the wafer arrangement method, and the like.

[Brief description of drawings]

FIG. 1 is a schematic view of a slide method boat used in Examples.

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Claims (3)

(57) [Claims] 1. A method for producing a gallium arsenide or aluminum gallium arsenide gallium arsenide semiconductor epitaxial wafer doped with silicon, wherein after the growth of the layer doped with silicon, the silicon is saturated in a gallium solution in an amount of 200 to 80.
A method for manufacturing a semiconductor epitaxial wafer, which comprises contacting at a temperature of 0 ° C. 2. The contact temperature is 300 ° C. to 700 ° C.,
The method according to claim 1, wherein the gallium solution is unsaturated in silicon. 3. The manufacturing method according to claim 1, wherein the gallium solution is brought into contact with the epitaxial wafer and then a slow cooling step is performed.