JPH0864567A - Surface treatment of epitaxial wafer - Google Patents

Abstract

PURPOSE: To enhance the velocity of dissolution of an Si crystal by a method wherein GaAs or GaAlAs epitaxial wafers with the Si crystal adhered on their surfaces are dipped in an HF tank of a specified concentration or higher in the range of a special temperature in the range of a special time and thereafter, are dipped in an aqueous solution, which is a strong alkali, and the Si crystal is selectively dissolved. CONSTITUTION: A wafer carrier 1, in which GaAs epitaxial wafers or GaAlAs epitaxial wafers With an Si crystal adhered on their surfaces are set, is dipped in an HF tank 2 of a concentration of 20% or higher at a temperature of 0 deg.C or higher and 50 deg.C or lower in a hour of 10 minutes or longer to 30 minutes or shorter and an oxide film on the surfaces adhered with the Si crystal is removed. After that, the wafer carrier 1 is rapidly moved to a pure water water tank 3 and after being dipped in the water tank 3 for about 10 seconds, the carrier 1 is moved to a KOH water tank 4, which is a strong alkali, the Si crystal is selectively dissolved and the dissolution of the Si crystal is made to accelerate more effectively. Thereby, the time to take for the dissolution of the Si crystal can be significantly shortened and the epitaxial wafers can be produced at lower cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for an epitaxial wafer which more efficiently promotes the dissolution of Si when the Si deposited on the surface of the epitaxial wafer is dissolved by an aqueous solution of a strong alkali. .

[0002]

2. Description of the Related Art Si-doped GaAlAs, Si-doped G
The aAs epitaxial wafer is used in a very large amount for infrared LEDs. These epitaxial wafers are produced by the liquid phase epitaxial growth method.

In the liquid phase epitaxial growth method, first, a GaAs substrate is mounted on a jig made of graphite.
In a separately provided growth solution reservoir, GaAs polycrystal, Si as a dopant, and Ga are set. Next, the jig is heated to about 900 ° C. in a hydrogen atmosphere, and the growth solution formed by dissolution in the growth solution reservoir is brought into contact with the GaAs substrate.
After that, the jig is gradually cooled to grow epitaxially on the surface of the GaAs substrate.

On the surface of the obtained epitaxial wafer,
Si deposited at about 600 ° C to 400 ° C is attached,
It cannot be made into a product as it is. Therefore, a method of polishing the surface of the epitaxial wafer or selectively etching and removing only Si by a wet process has been adopted (for example, JP-A-5-18249).

[0005]

The method of polishing an epitaxial wafer is more labor-intensive than the method of melting Si in a wet process, and thus the cost is high. On the other hand, if Si can be removed by a wet process, it is advantageous in terms of cost. This is because many sheets can be processed at once. However, in reality there are major problems in doing this. That is, the dissolution rate of Si is slow.

According to our experiments, even if the conditions are examined,
The dissolution rate of Si was at most 10 μm per hour. Moreover, the dissolution rate decreases with the passage of time. The size of the nucleus of Si actually deposited was about 50 to 100 μm, and when attempting to remove this Si crystal, it could not be removed even after 40 hours or more.

Therefore, in order to remove Si by the wet process, it is necessary to reduce the size of Si crystal. For this purpose, it is necessary to make the cooling rate after the epitaxial growth extremely slow. However, this means that the throughput decreases at the time of production, and the cost increase cannot be avoided.

An object of the present invention is to solve the above-mentioned problems of the prior art and to deposit S on the surface of an epitaxial wafer.
It is an object of the present invention to provide a surface treatment method for an epitaxial wafer that can more efficiently promote the dissolution of Si when i is dissolved by a wet process.

[0009]

The surface treatment method for an epitaxial wafer according to the present invention is performed on GaAs or GaAlAs.
Epitaxial wafers with a concentration of 2 above 0 ° C and below 50 ° C
By immersing in HF of 0% or more for 10 minutes to 30 minutes, or by immersing it in a mixed solution of Br and methanol for a certain time instead of HF for a certain period of time, it is a factor that reduces the dissolution rate of Si. After removing the oxide film on the surface, it is immersed in an aqueous solution of a strong alkali to selectively dissolve Si, thereby increasing the dissolution rate of Si.

Epitaxial wafers include GaAs or GaAlAs. KOH for strong alkali,
For example, NaOH.

[0011]

Function: The epitaxial wafer is immersed in H to remove the oxide film of Si and to avoid the formation of a new oxide film.
The temperature of F needs to be controlled in the range of 0 ° C to 50 ° C. This is because the solution freezes when the temperature is lower than 0 ° C.
This is because if the temperature is higher than 0 ° C., the rate of dissolution of Si in a strong alkaline aqueous solution will decrease.

The reason why the HF concentration is 20% or more is that
This is because if it is lower than 20%, the Si dissolution rate in the strong alkaline aqueous solution cannot be increased. Further, the reason why the time for immersing in HF is set to be 10 minutes or more and 30 minutes or less is that the Si dissolution rate in the strong alkaline aqueous solution decreases if it is shorter than 10 minutes and longer than 30 minutes.

Further, in order to avoid the slight oxidation and improve the dissolution efficiency of Si, the step of immersing in a mixed solution of HF or Br and methanol and the step of dissolving Si in a strong alkali are inactive. It may be performed in a gas, for example, nitrogen or Ar atmosphere.

Further, since the process of dissolving Si in strong alkali involves oxidation of Si, even if the epitaxial wafer is immersed in strong alkali for 60 minutes or more,
The surface of Si is again covered with the oxide film. To avoid this, the epitaxial wafer may be immersed in HF or a mixed solution of Br and methanol every 60 minutes.

[0015]

EXAMPLES Examples of the surface treatment method for an epitaxial wafer according to the present invention will be described below. FIG. 1 shows an apparatus configuration according to a first embodiment for carrying out the present invention. Reference numeral 1 is a wafer carrier, which is Si-doped G with Si attached to the surface.
This is a set of 10 aAs epitaxial wafers. 2 is an HF tank, 3 is a water tank containing pure water, and 4 is saturated K
A water tank containing an OH aqueous solution and 5 are water tanks containing pure water. The temperature of the HF tank 2 is controlled to 0 ° C to 50 ° C, the temperature of the KOH water tank 4 is controlled to 50 ° C to 100 ° C, and the temperature of the pure water tanks 3 and 5 is controlled to room temperature.

To dissolve Si, first, the wafer carrier 1 is left in the HF bath 2 for 10 to 30 minutes. After that, the wafer carrier 1 is immediately replaced with the pure water tank 3
Move to. After being immersed in the pure water tank 3 for 10 seconds, the wafer carrier 1 is transferred to the KOH water tank 4. Here, the dissolution of Si proceeds. After soaking in KOH water tank 4 for more than 60 minutes, S continues
When it is necessary to dissolve i, after 60 minutes, the wafer carrier 1 is transferred from the KOH water tank 4 to the pure water tank 5 and
After washing with water for a minute, it is returned to the HF water tank 2 again, and thereafter, the same operation as the beginning is repeated.

On the surface of the GaAs epitaxial wafer used for melting Si, Si crystals having a width of 50 to 100 μm and a height of about 50 μm were attached. This Si
The crystal was completely dissolved in 3 hours, and a flat GaAs surface having surface irregularities of several μm or less was obtained.

Now, the immersion conditions in the HF tank 2 described above will be examined. FIG. 2 is a graph showing the relationship between the time of immersion in HF and the subsequent dissolution rate of Si in KOH. The vertical axis represents the dissolution rate of Si, and the horizontal axis represents the time of immersion in HF. In addition, the dissolution rate of Si shown in the graph below is the same as the rate of Si immersed in the epitaxial wafer.
It is obtained from the change in the thickness of the substrate.

When the time for immersing the epitaxial wafer in HF is 10 minutes or less, the dissolution rate of Si is as low as 10 μm / h. On the other hand, when soaking for 10 minutes or more, the dissolution rate is 50 μm / h, which is five times higher. This is because the oxide film attached to the surface of Si is removed by HF.
However, after 30 minutes, the dissolution rate decreases again. The reason for this is that the water contained in the HF aqueous solution contains Si.
It is possible to reoxidize the surface of.

FIG. 3 shows H for immersing an epitaxial wafer.
It shows the relationship between the concentration of F and the subsequent dissolution rate of Si in KOH. In the figure, the vertical axis represents the dissolution rate of Si,
The horizontal axis represents the concentration of HF in the epitaxial wafer with respect to water. According to this, S in the present invention
In order to obtain the effect of increasing the dissolution rate of i, 20% or more H
F may be used. The effect of the present invention can be obtained only with HF of 20% or more. When the proportion of HF is small, the removal rate of the oxide film on the Si surface becomes smaller than the oxidation rate of the Si surface by water, and the oxidation is substantially reduced. This is probably because the film cannot be removed.

FIG. 4 shows H for immersing an epitaxial wafer.
It shows the relationship between the temperature of F and the Si dissolution rate when the epitaxial wafer is subsequently immersed in KOH. In the figure, the vertical axis represents the Si dissolution rate and the horizontal axis represents the HF temperature. According to this, when the temperature of HF rises to 50 ° C. or higher, the dissolution rate of Si decreases. This is because at a temperature of 50 ° C. or higher, the rate of oxidation of the Si surface by water increases. Therefore, to obtain the effect of the present invention, it is necessary to use HF at 50 ° C. or lower.

FIG. 5 shows the change over time in the dissolution rate of Si comparing the case of dissolving in strong alkali after being immersed in HF and the case of dissolving Si only in strong alkali without being immersed in HF. Is. The vertical axis represents the dissolution rate of Si and the horizontal axis represents K.
The time during which the epitaxial wafer is immersed in OH is shown. When Si is dissolved without being immersed in HF, the dissolution rate is as low as 10 μm / h from the beginning, and almost no dissolution occurs after 60 minutes or more. On the other hand, HF has 6
In the method of dissolving Si while soaking every 0 minutes, the dissolution rate of Si is as high as 50 μm / h from the beginning, and the dissolution rate of Si hardly decreases even after 60 minutes. This is because the oxide film formed on the surface of Si is removed.

As described above, according to the present embodiment, when Si is dissolved in the wet process, the dissolution rate of Si can be increased to about 5 times, which is suitable for promoting the dissolution of Si by a strong alkali. It can be said that it is a method.

Next, the second and third embodiments of the present invention will be described with reference to FIGS. 6 and 7.

In the case of FIG. 6 showing the second embodiment, the entire apparatus is housed in a box 11, and the inside of the box 11 is in an atmosphere in which Ar is purged. 6 is a wafer carrier, 7 is a water tank containing HF, 8 and 10 are water tanks containing pure water, and 9 is saturated KOH.
It is an aquarium containing an aqueous solution. In the KOH water tank 9, bubbles 12 of Ar are generated in water in order to reduce dissolved oxygen.

In order to dissolve Si with this apparatus, first, the wafer carrier 6 is immersed in the HF bath 7 for 10 to 30 minutes. After that, is immediately transferred to the pure water tank 8. Pure aquarium 8 to 10
After soaking for a second, the wafer carrier 6 is transferred to the KOH water tank 9. Here, the dissolution of Si proceeds. After soaking for a predetermined time,
The KOH water tank 9 is moved to the pure water tank 10 and washed with water for 1 minute. In this device, the atmosphere is purged with Ar and K
Since the bubbles 12 of Ar are generated in the OH water tank 9, after the oxide film on the Si surface is removed once, the oxidation of the Si surface hardly progresses, and it is not necessary to immerse the HF tank 7 again. The atmosphere gas and the bubbles may be N ₂ gas in addition to Ar.

On the surface of the GaAs epitaxial wafer used for melting Si, Si crystals having a width of 50 to 100 μm and a height of about 50 μm were attached. The time required for melting the Si crystal on the surface with this apparatus was one and a half hours.

According to the method shown in FIG. 7 according to the third embodiment, as shown in FIG.
2 is that a 1: 1 mixed solution of Br and methanol is used instead of HF as a solution for removing the oxide film on the Si surface. 13 is a wafer carrier, 14 is HF
Tanks, 15 and 17 are water tanks containing pure water, and 16 is saturated KOH
It is an aquarium containing an aqueous solution. In this device, first, HF
The epitaxial wafer is immersed in a mixed solution of Br and methanol for 10 minutes instead of. The other operations are the same as those of the apparatus described so far.

On the surface of the GaAs epitaxial wafer used to dissolve Si, Si crystals having a width of 50 to 100 μm and a height of about 50 μm were attached. The time required to dissolve the Si crystal on the surface with this apparatus was 5 hours.

[0030]

According to the present invention, after removing the Si oxide film with HF or a mixed solution of Br and methanol, S
Since i is melted, the time required for melting Si can be significantly reduced, and an epitaxial wafer can be produced at a lower cost.

[Brief description of drawings]

FIG. 1 is a structural diagram of a Si melting apparatus according to a first embodiment for carrying out a method for treating a surface of an epitaxial wafer according to the present invention.

FIG. 2 is a graph showing the relationship between the time of immersion in HF and the dissolution rate of Si.

FIG. 3 is a graph showing the relationship between the concentration of HF and the dissolution rate of Si.

FIG. 4 is a graph showing the relationship between the temperature of HF and the dissolution rate of Si.

FIG. 5 is a graph showing changes in the dissolution rate of Si with the lapse of time for immersion in KOH.

FIG. 6 is a structural diagram of a Si melting apparatus for explaining a second embodiment of the present invention.

FIG. 7 is a structural diagram of a Si melting apparatus for explaining a third embodiment of the present invention.

[Explanation of symbols]

 1 wafer carrier 2 HF tank 3 water tank containing pure water 4 water tank containing saturated KOH aqueous solution 5 water tank containing pure water

Claims (4)

[Claims] 1. GaAs having Si crystals adhered to its surface
After immersing the epitaxial wafer or the GaAlAs epitaxial wafer in HF having a temperature of 0 ° C. to 50 ° C. and a concentration of 20% or more for 10 minutes to 30 minutes,
A method for surface treatment of an epitaxial wafer, which comprises selectively dissolving Si in an aqueous solution of a strong alkali. 2. GaAs having Si crystals adhered to its surface
Or an GaAlAs epitaxial wafer is immersed in a mixed solution of Br and methanol for a certain period of time, and then Si is selectively dissolved in an aqueous solution of a strong alkali. 3. The method for surface treatment of an epitaxial wafer according to claim 1, wherein when the dissolution time of the strong alkali in an aqueous solution exceeds 60 minutes, the HF or Br and methanol are added every 60 minutes. And a step of dissolving it in an aqueous solution of a strong alkali are repeated. 4. The method for surface treatment of an epitaxial wafer according to claim 1, wherein all steps are performed in an atmosphere purged with an inert gas.