JPH11126766A - Method for cleaning semiconductor crystal wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cleaning a semiconductor crystal wafer by which a very small quantity of impurities remaining on the mirror plane of a semiconductor crystal wafer whose surface is mirror-polished can be perfectly cleaned off and removed, and no conductive layer is formed at interface between the wafer and an epitaxial functional layer when the epitaxial functional layer is grown on the mirror-polished surface of the semiconductor crystal wafer. SOLUTION: A semiconductor crystal wafer whose surface is mirror-polished is immersed in an ultra pure water with dissolved ozone in which 0.5 ppm or higher concentration of ozone is dissolved, an ultra pure water solution with 20% of HF or an ultra pure water solution with 20% of ammonia irradiated with light having energy equal to or larger than a band gap. Then, the wafer is cleaned with an acid solution, an alkaline solution or a mixed acid- alkaline solution and then is cleaned with an ultra pure water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a semiconductor crystal wafer.

[0002]

2. Description of the Related Art Compound semiconductors are widely used as basic materials for various elements such as Schottky gate field effect transistors (MESFETs), high mobility transistors (HEMTs), heterojunction bipolar transistors (HBTs), and light emitting / receiving devices. .

In these various devices, an epitaxial functional layer suitable for each application is formed on a mirror-polished surface of a compound semiconductor crystal wafer, for example, a GaAs crystal wafer, by a metal organic vapor phase epitaxy (MOVPE) or a molecular beam epitaxy (MBE). And so on.

Conventionally, compound semiconductor crystal wafers such as G
The surface of the aAs crystal wafer was mirror-finished as follows.

First, a material compound semiconductor crystal ingot is sliced, and a GaAs crystal wafer is cut out.

Next, the surface of the cut GaAs crystal wafer is roughly polished with alumina abrasive grains. This rough polishing improves the flatness of the GaAs crystal wafer.

Next, the surface of the roughly polished GaAs crystal wafer is mirror-finished by mechanochemical polishing.

Next, the polished GaAs crystal wafer is degreased and cleaned.

Next, the degreased and cleaned GaAs crystal wafer is cleaned with a cleaning liquid having an extremely slight etching action, and then cleaned with ultrapure water.

Next, the GaAs crystal wafer washed with ultrapure water is dried by an isopropyl alcohol drying method or a spin drying method.

In the epitaxial growth, G at this stage is used.
Although an aAs crystal wafer can be used, a GaAs crystal wafer to which the following steps are added for removing impurities on the surface is usually used for epitaxial growth.

The dried GaAs crystal wafer obtained as described above is used as a sulfuric acid-based etchant (H ₂ SO ₄ —H ₂ O ₂ —
H ₂ O) or ammonia-based etchant (NH ₄ O)
H—H ₂ O ₂ —H ₂ O) to make the wafer surface 1 to 2
Etch μm.

Next, the GaAs crystal wafer whose surface is etched by 1 to 2 μm is washed with ultrapure water.

Finally, the GaAs crystal wafer washed with ultrapure water is dried by an isopropyl alcohol drying method, a spin drying method, or a nitrogen gas spray drying method.

That is, a GaAs crystal wafer at this stage is usually used for epitaxial growth.

The above-mentioned GaAs crystal wafer is thermally oxidized to form a thick oxide film containing impurities on the surface, and then the GaAs crystal wafer having the oxide film formed on the surface is epitaxially grown. There has also been reported a method of removing the oxide film by heat treatment in an apparatus to remove impurities on the surface.

[0017]

However, even a GaAs crystal wafer that has been cleaned and dried up to the above stage or a GaAs crystal wafer from which a thermal oxide film has been removed, a very small amount of impurities remains on the mirror surface of the wafer. I understand that it is.

For example, in a GaAs crystal wafer in which an extremely small amount of Si remains as an impurity on the mirror surface of a wafer, an epitaxial functional layer is grown on the mirror surface of the GaAs crystal wafer. It becomes a mold carrier, and as a result, a conductive layer is formed at the interface. In a Schottky gate field effect transistor (MESFET) manufactured using a GaAs crystal wafer having an epitaxial functional layer having such a conductive layer formed thereon, a leak current flows due to the conductive layer at the interface between the epitaxial functional layer and the wafer. As a result, it has been found that the electrical characteristics of the transistor deteriorate.

The present invention has been made in view of such a point, and an object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to leave a mirror-polished surface of a semiconductor crystal wafer on a mirror surface of a semiconductor crystal wafer. Completely cleaning the trace amount of impurities
A method of cleaning a semiconductor crystal wafer which can be removed, thereby eliminating the formation of a conductive layer at the interface between the epitaxial functional layer and the wafer when the epitaxial functional layer is grown on the mirror surface of the semiconductor crystal wafer. It is in.

[0020]

The gist of the present invention is to provide a semiconductor crystal wafer having a mirror-polished surface.
After being immersed in ozone-dissolved ultrapure water or 20% HF ultrapure aqueous solution or 20% ammonia ultrapure aqueous solution having a dissolved ozone concentration of 0.5 ppm or more and irradiated with light having an energy greater than the band gap, an acid solution or an alkaline solution Alternatively, there is provided a method for cleaning a semiconductor crystal wafer, characterized by cleaning with a mixed solution of an acid and an alkali, and then cleaning with ultrapure water.

In the present invention, the semiconductor crystal wafer is
III-V compound semiconductors or II-VI compound semiconductors are preferred. Here, a GaAs semiconductor or the like is used as the III-V group compound semiconductor. In addition, the II-VI group compound semiconductor includes InP and the like.

In the present invention, the light having energy equal to or greater than the band gap is preferably light from a halogen lamp.

In the present invention, the acid solution is preferably one or a mixture of two or more selected from HCl (hydrochloric acid), HF (hydrofluoric acid) and H ₂ SO ₄ (sulfuric acid).

In the present invention, the alkaline solution is preferably aqueous ammonia, an organic amine solution, or a mixed solution thereof.

In the present invention, a semiconductor crystal wafer having a mirror-polished surface is treated with a dissolved ozone concentration of 0.5 ppm irradiated with light having an energy not less than the band gap.
The cleaning with ozone-dissolved ultrapure water, 20% HF ultrapure aqueous solution, or 20% ammonia ultrapure aqueous solution is performed for the following reason.

In this method, first, a semiconductor crystal wafer having a mirror-polished surface is immersed in ozone-dissolved ultrapure water to make the semiconductor crystal wafer have a thickness of about several nm on the mirror surface of the semiconductor crystal wafer. An oxide film is formed, and then the oxide film formed on the mirror surface of the semiconductor crystal wafer is dissolved and washed with an acid solution, an alkali solution, or a mixed solution of an acid and an alkali, so that the oxide film remains on the mirror surface of the semiconductor crystal wafer. A very small amount of impurities was dissolved and washed, and then completely cleaned by washing with ultrapure water.

In this method, a semiconductor crystal wafer whose surface is mirror-polished is first immersed in a 20% HF ultrapure aqueous solution to leave the semiconductor crystal wafer on the mirror surface of the semiconductor crystal wafer. Dissolve and wash only trace impurities, then completely dissolve and wash with acid solution or alkali solution or mixed solution of acid and alkali, and then completely clean by washing with ultrapure water .

In this method, a semiconductor crystal wafer whose surface has been mirror-polished is first immersed in a 20% ammonia ultrapure aqueous solution to remain on the mirror surface of the semiconductor crystal wafer. Dissolve and wash only trace impurities, then completely dissolve and wash with acid solution or alkali solution or mixed solution of acid and alkali, and then completely clean by washing with ultrapure water .

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment and a comparative example of a method for cleaning a semiconductor crystal wafer according to the present invention will be described.

Example 1 First, a semi-insulating GaAs wafer having a crystal orientation (100) was prepared by mirror-polishing the surface by a conventional method, and then washed and dried.

Next, the prepared semi-insulating GaAs
The wafer was immersed in ozone-dissolved ultrapure water having a dissolved ozone concentration of 0.5 ppm for 10 minutes. During this immersion, the ozone-dissolved ultrapure water was irradiated with light from a halogen lamp.

Next, the semi-insulating GaAs arsenic wafer taken out of the ozone-dissolved ultrapure water is placed in a 30% hydrochloric acid aqueous solution for 5 minutes.
Soak for minutes.

Next, the semi-insulating GaAs wafer taken out of the 30% hydrochloric acid aqueous solution was completely washed with ultrapure water.

Next, semi-insulating Ga washed with ultrapure water
The As wafer is dried by a spin drying method.

Next, the semi-insulating Ga obtained above
On the mirror surface of the As wafer, an epitaxial functional layer was grown by metal organic vapor phase epitaxy (MOVPE) to grow undoped GaAs to 500 nm and Si-doped GaAs (carrier concentration: 2 × 10 ¹⁷ cm ⁻³ ) to 200 nm.

Example 2 A semi-insulating GaAs wafer provided with an epitaxial functional layer was obtained in the same manner as in Example 1 except that ozone-dissolved ultrapure water having a dissolved ozone concentration of 1 ppm was used.

(Example 3) The dissolved ozone concentration is 1.5 ppm
A semi-insulating GaAs wafer provided with an epitaxial functional layer was obtained in the same manner as in Example 1 except that the ozone-dissolved ultrapure water was used.

(Example 4) The dissolved ozone concentration is 2.0 ppm
A semi-insulating GaAs wafer provided with an epitaxial functional layer was obtained in the same manner as in Example 1 except that the ozone-dissolved ultrapure water was used.

Example 5 Instead of ozone-dissolved ultrapure water, 2
A semi-insulating GaAs wafer provided with an epitaxial functional layer was obtained in the same manner as in Example 1 except that a 0% HF ultrapure aqueous solution was used.

Example 6 Instead of ozone-dissolved ultrapure water, 2
Semi-insulating GaAs provided with an epitaxial functional layer in the same manner as in Example 1 except that a 0% ammonia ultrapure aqueous solution was used.
s wafer was obtained.

Comparative Example 1 A semi-insulating GaAs wafer provided with an epitaxial functional layer was obtained in the same manner as in Example 1 except that only ozone-dissolved ultrapure water having a dissolved ozone concentration of 0 ppm, that is, ultrapure water was used. Was.

(Comparative Example 2) The dissolved ozone concentration is 0.1 ppm
A semi-insulating GaAs wafer provided with an epitaxial functional layer was obtained in the same manner as in Example 1 except that the ozone-dissolved ultrapure water was used.

(Comparative Example 3) The dissolved ozone concentration was 0.3 ppm
A semi-insulating GaAs wafer with an epitaxial functional layer was obtained in the same manner as in Example 1 except that the ozone-dissolved ultrapure water was used.

(Characteristic test) Next, with respect to the semi-insulating GaAs wafers with an epitaxial functional layer obtained in Examples 1 to 4 and Comparative Examples 1 to 3 described above, the electric properties at the interface between the epitaxial functional layer and the GaAs wafer were measured. Characteristics and interface impurities were analyzed.

Here, the electric characteristics were measured by the CV method.

Further, impurities at the interface are formed by SIMS.
The i concentration was analyzed.

FIG. 1 shows the dissolved ozone concentration of the ozone-dissolved ultrapure water used for cleaning and the epitaxial functional layer / GaAs of the obtained semi-insulating GaAs wafer with an epitaxial functional layer.
4 is a graph showing a relationship with a wafer interface carrier concentration (cm ⁻³ ).

In the graph of FIG. 1, the dissolved ozone concentration of the ozone-dissolved ultrapure water is within the range of 0 to 2.0 ppm. The data for a semi-insulating GaAs wafer with an epitaxial functional layer prepared by cleaning with ultrapure water is also described.

As can be seen from FIG. 1, the semi-insulating GaAs wafers with the epitaxial functional layer of Comparative Examples 1 to 3 have the carrier concentration (c) at the interface between the epitaxial functional layer and the GaAs wafer.
m- ³ ) is a major drawback. Such a semi-insulating GaAs wafer with an epitaxial functional layer having a large carrier concentration (cm ⁻³ ) at the interface between the epitaxial functional layer and the GaAs wafer has a conductive layer at the interface between the epitaxial functional layer and the wafer, and as a result, the leakage current Is likely to flow, thereby significantly deteriorating the electrical characteristics of the transistor when it is manufactured.

On the other hand, the semi-insulating GaAs wafers with an epitaxial functional layer of Examples 1 to 4 have a carrier concentration (cm ^-3 ) at the interface between the epitaxial functional layer and the GaAs wafer which is practically no problem, that is, 4 × 10 ^13. It was significantly reduced to cm ^-3 . Although data is not shown, Examples 1 to 4
The transistor manufactured from the semi-insulating GaAs wafer with the epitaxial function layer described above exhibited excellent electrical characteristics and reliability.

Although data is not shown, the fifth embodiment
And semi-insulating GaAs with an epitaxial functional layer according to Example 6.
For the s wafer, the carrier concentration (cm ^-3 ) at the interface between the epitaxial functional layer and the GaAs wafer was remarkably reduced to a practically ^acceptable level, that is, 4 × 10 ¹³ cm ^-3 . Example 5
And semi-insulating GaAs with an epitaxial functional layer according to Example 6.
Transistors fabricated from s wafers also exhibited excellent electrical properties and reliability.

Table 1 shows the results of analysis of impurities at the interface by the SIMS method.

[0053]

[Table 1]

As can be seen from Table 1, the interface between the semi-insulating GaAs wafers with the epitaxial functional layers of Comparative Examples 1 to 3 has a disadvantage that the Si concentration is abnormally high.

On the other hand, the Si concentration at the interface of the semi-insulating GaAs wafer with the epitaxial functional layer of Examples 1-4 is N.P. D (measurement lower limit of 5 × 10 ¹⁵ cm ⁻³ or less), which indicates that Si, an impurity remaining on the mirror surface of the semi-insulating GaAs wafer, was effectively cleaned and removed.

Although data is not shown, the semi-insulating GaAs with an epitaxial functional layer of the fifth and sixth embodiments was used.
The Si concentration of the wafer is also N.I. D (5 × 10 ¹⁵ cm ^{−3 of the} lower limit of measurement)
From the above, it was found that the impurity Si remaining on the mirror surface of the semi-insulating GaAs wafer was effectively cleaned and removed.

[0057]

According to the method for cleaning a semiconductor crystal wafer of the present invention, a trace amount of impurities remaining on the mirror surface of the semiconductor crystal wafer whose surface has been mirror-polished can be completely cleaned and removed. Schottky gate field-effect transistor (ME) manufactured based on a semiconductor crystal wafer
SFET), high mobility transistor (HEMT), heterojunction bipolar transistor (HBT), and the performance of various elements such as a light emitting / receiving device can be remarkably improved, and is industrially useful.

[Brief description of the drawings]

FIG. 1 shows the dissolved ozone concentration of ozone-dissolved ultrapure water and the epitaxial functional layer / Ga of a semi-insulating GaAs wafer with an epitaxial functional layer immersed in the ozone-dissolved ultrapure water.
5 is a graph showing a relationship with an As wafer interface carrier concentration (cm ^-3 ).

Claims (8)

[Claims] An oxide film is formed by immersing a semiconductor crystal wafer having a mirror-polished surface in ozone-dissolved ultrapure water having a dissolved ozone concentration of 0.5 ppm or more, which is irradiated with light having an energy of a band gap or more. After the formation, the oxide film is dissolved and washed with an acid solution, an alkali solution or a mixed solution of an acid and an alkali, and then washed with ultrapure water. 2. The method according to claim 1, wherein the semiconductor crystal wafer is a III-V compound semiconductor. 3. The method according to claim 1, wherein the semiconductor crystal wafer is a II-VI compound semiconductor. 4. The method for cleaning a semiconductor crystal wafer according to claim 1, wherein the light having energy equal to or larger than the band gap is light of a halogen lamp. 5. The method for cleaning a semiconductor crystal wafer according to claim 1, wherein the acid solution is one or a mixture of two or more selected from hydrochloric acid, hydrofluoric acid and sulfuric acid. 6. The method for cleaning a semiconductor crystal wafer according to claim 1, wherein the alkaline solution is aqueous ammonia, an organic amine solution, or a mixed solution thereof. 7. A semiconductor crystal wafer having a mirror-polished surface is immersed in a 20% HF ultrapure aqueous solution, washed with an acid solution, an alkali solution, or a mixed solution of an acid and an alkali, and then washed with ultrapure water. A method for cleaning a semiconductor crystal wafer, comprising cleaning. 8. A semiconductor crystal wafer whose surface has been mirror-polished is immersed in a 20% ammonia ultrapure aqueous solution, washed with an acid solution, an alkali solution or a mixed solution of an acid and an alkali, and then washed with ultrapure water. A method for cleaning a semiconductor crystal wafer, comprising cleaning.