JPH07211688A - Production of compound semiconductor substrate - Google Patents

Abstract

PURPOSE:To prevent accumulation of electrically active carriers on the interface between a substrate and an epitaxial film when the epitaxial film is grown on the surface of a produced compound semiconductor substrate. CONSTITUTION:A thin compound semiconductor substrate is cleaned and then oxidized to deposit an oxide on the surface thereof. Subsequently, the oxide is removed and the substrate is dried. The oxide is deposited, for example, by immersing the substrate into an oxidizing agent having oxidizing power, e.g. a hydrogen peroxide water. The oxide is removed by immersing the substrate into an oxide removing agent having no oxidizing power, e.g. ammonia water, aqueous solution of sodium hydroxide, phosphoric acid, hydrochloric acid or hydrofluoric acid. This method prevents accumulation of electrically active carriers on the interface between a compound semiconductor substrate and an epitaxial film and uneven drying simultaneously.

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 a compound semiconductor substrate, and more particularly to a technique useful when applied to a cleaning / drying process of a GaAs substrate or an InP substrate after mirror polishing or etching.

[0002]

2. Description of the Related Art Generally, a compound semiconductor substrate (wafer) cut from a single crystal ingot of GaAs or InP, for example, has its surface mirror-finished, followed by degreasing and cleaning with an organic solvent such as trichlene, ketone, alcohol, etc. After being rinsed with water, it is dried. Conventionally, as a method for drying a substrate, a spin drying method in which a substrate is rotated at a high speed and water droplets are blown by its centrifugal force, a steam drying method in which a substrate surface is heated by steam to be dried, and the like are known. These drying methods are also used in the substrate cleaning / drying process after the etching process.

[0003]

However, when an epitaxial film is grown on the surface of a GaAs substrate or an InP substrate dried by the above-mentioned conventional drying method by MOCVD (metalorganic chemical vapor deposition) or the like, the growth occurs. There is a problem in that electrically active carriers (impurities) are accumulated at the interface between the epitaxial film and the substrate, and the carrier concentration becomes higher than the design value of the semiconductor device formed on the substrate. Particularly, in the case of a device using a semi-insulating substrate, the carrier concentration at the interface needs to be 5 × 10 ¹⁴ cm ⁻³ or less.

Ga dried by the above conventional drying method is also used.
On the As substrate, if the water content on the substrate surface is not sufficiently removed during drying, contamination of aggregates of fine particles, called so-called drying unevenness, occurs on the substrate surface, and the contamination significantly increases the surface quality of the substrate. It was sometimes lowered. This unevenness of drying adheres strongly to the substrate, and in order to remove it, the dried substrate had to be re-polished and washed and dried to prevent unevenness in drying. There was a problem that it took time.

In the case of a Si semiconductor substrate cut out from a Si single crystal ingot, the substrate is H ₂ O ₂ -N
H ₄ OH solution (first solution) and H ₂ O ₂ —HCl solution ( _second solution)
Liquid), so-called RCA cleaning method, and its RCA
In the cleaning, an improved method of RCA cleaning in which the substrate is immersed in the first liquid, then in the HF solution, and then in the second liquid,
So-called SE (slitch etch) cleaning, in which the substrate surface is shallowly etched by immersing the substrate in an HNO ₃ —HF-based solution whose temperature is controlled at an extremely low HF concentration, has been proposed. Although the effect of reducing the impurity concentration is expected, the effect was not always satisfactory when the impurity concentration on the substrate surface after cleaning was compared with the impurity concentration in the bulk of the Si single crystal.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a substrate and an epitaxial film when an epitaxial film is grown on the surface of a manufactured compound semiconductor substrate. It is an object of the present invention to provide a method for manufacturing a compound semiconductor substrate capable of preventing the accumulation of electrically active carriers at the interface of the above.

Another object of the present invention is to provide a method for manufacturing a compound semiconductor substrate, which makes it possible to apply a spin drying method without causing unevenness of drying on the substrate surface in the step of cleaning and drying the compound semiconductor substrate. It is to be.

[0008]

In order to achieve the above object, the present inventor has conducted a detailed study on uneven drying, and in the case of a GaAs substrate, for example, a chemical reaction that occurs during washing of the substrate causes It is considered that foreign matter such as poorly water-soluble metallic arsenic (As) is generated on the surface of the substrate, and the metallic arsenic oxidizes during the drying of the substrate to form arsenic oxide (As ₂ O ₃ ) and uneven drying occurs. It was Therefore, after washing with water and before drying, the surface of the substrate is once oxidized to be covered with an oxide film, and then the oxide film is removed, whereby foreign matters such as the metal As are removed and uneven drying is prevented. An invention that has the effect of being produced was first filed (Japanese Patent Application No. 5-115063).

After this, the present inventor has made a detailed study on the accumulation of electrically active carriers at the interface between the substrate and the epitaxial film. As a result, for example, in the case of an InP substrate, the chemistry that occurs during the washing of the substrate with water. It was found that foreign matter such as poorly water-soluble single phosphorus (P) is generated on the surface of the substrate by the reaction, and impurities in the single phosphorus are reduced at the time of forming the epitaxial film and accumulated on the interface. Therefore, the present inventor
By applying the invention of the above-mentioned Japanese Patent Application No. 5-115063, it is thought that foreign substances such as elemental phosphorus can be removed from the substrate surface before drying the substrate, and as a result of intensive studies, The invention was completed.

The present invention has been made on the basis of the above-mentioned findings and the like, and after cleaning a thin plate-like substrate made of a compound semiconductor, the substrate is oxidized to cover the surface of the substrate with an oxide film, and the oxidation thereof is performed. A method is provided for removing the film and then drying the substrate.

The oxide film covering the surface of the substrate is removed by, for example, an oxide removing agent having no oxidizing power, specifically, ammonia water (NH ₄ OH) and sodium hydroxide (NaO).
H) The substrate is dipped in an aqueous solution, phosphoric acid (H ₃ PO ₄ ), hydrochloric acid or hydrofluoric acid. The oxide removing agent is not limited to those listed as examples, and may be any one as long as it has a high solubility in an oxide (oxide film) and does not newly generate an oxide on the substrate surface.

Further, as a specific method for oxidizing the substrate surface, hydrogen peroxide solution (H ₂ O ₂ ) or nitric acid (HNO ₃ ) is used.
Examples include a method of immersing the substrate in an oxidizing agent having an oxidizing power such as ozone and ozone (O ₃ ), or a method of thermally oxidizing the substrate by UV (ultraviolet) irradiation or steam drying. Alternatively, the substrate may be left in the air for several hours, for example, 3 to 24 hours to be naturally oxidized.

Needless to say, the method of manufacturing a compound semiconductor substrate according to the present invention can be used not only for cleaning and drying the substrate by spin drying, but also for other substrate drying methods such as vapor drying. Absent. Further, it is needless to say that it is effective not only in the cleaning / drying of the substrate performed after the mirror polishing process but also in the cleaning / drying of the substrate performed after the etching process.

[0014]

According to the above means, after the compound semiconductor substrate is washed and before being dried, the surface of the substrate is once oxidized to cover the surface with an oxide film, and the oxide film is removed. Foreign matter (eg, simple substance P or metal As)
Etc. can be removed together with the oxide film, so that not only the spin drying method but also other drying methods can be carried out at an electrical interface at the interface between the substrate and the epitaxial film, which has been conventionally caused by the foreign matter. It is possible to prevent the accumulation of highly active carriers, and at the same time to prevent the occurrence of uneven drying.

Further, according to the above means, when the oxide film once formed is removed, the surface of the substrate is removed in a minute amount, for example, about several tens of angstroms. Therefore, the present invention can be used as an alternative to a minute amount of etching means. It is valid.

[0016]

EXAMPLES The features of the present invention will be clarified below with reference to Examples and Comparative Examples. In the examples and comparative examples, the concentration of electrically active carriers at the interface between the substrate and the epitaxial film (hereinafter referred to as “interface carrier concentration”) was measured by the C / V method. In the examples and the comparative examples, as the substrates before the epitaxial growth, both GaAs substrates and InP substrates were semi-insulating substrates (specific resistance of 10 ⁷ Ωcm or more).

(Embodiment 1) First, a raw material and a liquid sealant are put in a crucible, the raw material and the liquid sealant are heated by a heater to be melted, and the raw material melt is made of a seed composed of a GaAs single crystal. Gradually pull up while contacting and rotating the crystals,
A GaAs single crystal ingot having a diameter of 4 inches in the straight body was grown.

From the grown ingot, a substrate having a (100) plane as a main surface and a thickness of 1 mm was cut out, and etching treatment, lapping treatment, etching treatment,
After sequentially performing polishing processing, the substrate was degreased and washed with isopropyl alcohol, and further rinsed with ultrapure water to make the surface mirror-finished.

Then, the GaAs substrate is, for example,
Immerse in 0.1% H ₂ O ₂ water (oxidizer) for 30 seconds to form an oxide film on the substrate surface, then wash with water, and then add 0.1%.
The above oxide film was removed by immersing it in NH ₄ OH water (oxide removing agent) for 2 minutes. After the substrate was washed again with water, it was dried by a spin drying method similar to the conventional one.

GaAs substrate 1 obtained by the above procedure
After observing the 00 sheets and observing the surface immediately after drying,
No unevenness in drying was observed on all the substrates. In addition, even after a lapse of time (for example, the next day), uneven drying did not occur.

Further, by a well-known laser beam irradiation type particle counter, 0.2 μm adhered to the surface of the substrate.
When the number of fine particles having the above particle diameters was measured, the number was 0.3 per square centimeter on average. This number did not change over time (eg, the next day).

On the GaAs substrate which has undergone the above-mentioned procedure, ie, degreasing cleaning, rinsing cleaning, oxide film formation with H ₂ O ₂ water, oxide film removal with NH ₄ OH water, water cleaning and spin drying. An epitaxial film of GaAs was grown by the MOCVD method. The thickness of the epitaxial film was 0.7 μm, and the growth temperature was 725 ° C.

The obtained G with an GaAs epitaxial film
The interface carrier concentration of the aAs substrate was 2 × 10 ¹⁴ cm ⁻³ , which was a carrier concentration at a level without any problem. That is, it was confirmed that electrically active carriers were not generated at the interface between the substrate and the epitaxial film.

Example 2 100 GaAs substrates having mirror-finished surfaces were obtained in the same procedure as in Example 1 above. However, in Example 2, instead of the spin drying method of Example 1,
Steam drying method with isopropyl alcohol (boiling point: 82 ° C)
The substrate was dried according to (1). The other substrate manufacturing conditions, manufacturing procedures, and the like were the same as in Example 1 above.

As a result, no unevenness in drying was observed in all the GaAs substrates, and no unevenness in drying occurred even after a lapse of time. The number of fine particles measured by the particle counter was 0.4 per square centimeter on average, and the number did not change even when measured the next day. In Example 2, epitaxial growth was not performed, and therefore, the interfacial carrier concentration of the substrate was not measured.

(Comparative Example 1) By the same procedure as in Example 1 above, 100 GaAs substrates each having a mirror-finished surface were obtained. In Comparative Example 1, the substrate was rinsed with ultrapure water and immediately spin-dried without forming and removing the oxide film by immersion in H ₂ O ₂ water and NH ₄ OH water. Dried. The other substrate manufacturing conditions, manufacturing procedures, and the like were the same as in Example 1 above.

When the surface of the substrate was observed immediately after drying, no unevenness in drying was observed in all the GaAs substrates. However, when the surface was observed again the next day, 70 out of 100 substrates, that is, 70% of the substrates were observed. There was uneven drying. Further, when measured by a particle counter, the number of fine particles having a particle diameter of 0.2 μm or more was 170 per square centimeter on average. In addition, this Comparative Example 1
Then, the interface carrier concentration of the substrate was not measured.

(Comparative Example 2) By the same procedure as in Example 1 above, 100 GaAs substrates each having a mirror-finished surface were obtained. In Comparative Example 2, the substrate was rinsed with ultrapure water and rinsed with NH ₄ OH water without forming and removing the oxide film by immersion in H ₂ O ₂ water and NH ₄ OH water. The substrate surface was washed by immersing it in a mixed solution of H ₂ O ₂ water for 0.5 minutes, washed with water, and then dried by a spin drying method. At that time, the concentration of the mixed solution used was as follows. NH ₄ OH: 0.1%, H ₂ O ₂ : 0.1% Other manufacturing conditions and manufacturing procedures for the substrate were the same as in Example 1 above.

The obtained G with an GaAs epitaxial film
The interface carrier concentration of the aAs substrate is 2 × 10 ¹⁵ to 1 × 10
^{It was 17} cm ⁻³ , which was higher than the carrier concentration of the GaAs substrate alone. That is, it was found that electrically active carriers were generated at the interface between the substrate and the epitaxial film. In addition, in this Comparative Example 2, the presence or absence of occurrence of drying unevenness was not observed.

(Embodiment 3) Using an InP single crystal as a seed crystal, the same growth method (liquid-sealed Czochralski method) as in the above-mentioned Embodiment 1 was used and Fe (iron) -doped InP single crystal having a diameter of 2 inches in the straight body portion was used. A crystal ingot was grown. From the grown ingot, a substrate having a (100) plane as a main surface and a thickness of 1 mm was cut out and rinsed by the same procedure as in Example 1 above to make the surface mirror-finished.

Subsequently, the InP substrate is dipped in, for example, 3% by weight of H ₂ O ₂ water (oxidizing agent) for 3 minutes to form an oxide film on the surface of the substrate, washed with water, and further washed with 8% by weight. H ₃
The oxide film was removed by immersing it in a PO ₄ aqueous solution (oxide removing agent) for 3 minutes. The substrate was washed again with water and then dried as in the conventional case.

On the obtained InP substrate, an InP epitaxial film having a thickness of 1 μm was grown at a growth temperature of 660 ° C. by the MOCVD method. The interface carrier concentration of the InP substrate with the InP epitaxial film was 2 × 10 ¹⁴ cm ⁻³ , and it was confirmed that electrically active carriers were not generated at the interface between the substrate and the epitaxial film.

Generally, in the InP substrate, the Ga
Since the drying unevenness unlike the As substrate hardly occurs, the substrate surface was not observed for the drying unevenness.

(Fourth Embodiment) The same procedure as in the third embodiment is used.
An InP substrate with an nP epitaxial film was obtained. However, in the fourth embodiment, the rinse cleaning step and H ₂ O _{2 of the} above-mentioned third embodiment are performed.
During the process of forming an oxide film with water, H ₃ PO ₄ water and H ₂ O ₂ are added.
The substrate surface was washed by immersing the substrate in a mixed solution of water for 5 minutes. At that time, the volume ratio of the mixed solution used was as follows. H ₃ PO ₄ : H ₂ O ₂ : H ₂ O = 20: 5: 1 Other substrate manufacturing conditions, manufacturing procedures, etc. were the same as in Example 3 above.

InP with the obtained InP epitaxial film
The interface carrier concentration of the P substrate was 7 × 10 ¹³ cm ⁻³ , and it was confirmed that electrically active carriers were not generated at the interface between the substrate and the epitaxial film.

(Comparative Example 3) In the same procedure as in Example 3 above, I
An InP substrate with an nP epitaxial film was obtained. In Comparative Example 3, the substrate was rinsed with ultrapure water and then dried without forming and removing the oxide film by immersion in H ₂ O ₂ water and H ₃ PO ₄ water. Other manufacturing conditions, manufacturing procedures, etc. of the substrate were the same as those in the third embodiment.

InP with the obtained InP epitaxial film
The interface carrier concentration of the P substrate was 3 × 10 ¹⁶ cm ⁻³ , and it was found that electrically active carriers were generated at the interface between the substrate and the epitaxial film.

(Comparative Example 4) The same procedure as in Example 4 was repeated.
An InP substrate with an nP epitaxial film was obtained. In addition, in this Comparative Example 4, the substrate surface was exposed to H ₂ O without forming and removing the oxide film by immersion in H ₂ O ₂ water and H ₃ PO ₄ water.
After washing with a mixed solution of ₃ PO ₄ water and H ₂ O ₂ water, it was washed with water and dried. Other manufacturing conditions, manufacturing procedures, etc. of the substrate were the same as those in the fourth embodiment.

InP with the obtained InP epitaxial film
The interface carrier concentration of the P substrate was 4 × 10 ¹⁶ cm ⁻³ , and it was found that electrically active carriers were generated at the interface between the substrate and the epitaxial film.

The results of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in Table 1. As is clear from the table, by manufacturing the semiconductor substrate to which the present invention is applied, it is possible to prevent the accumulation of electrically active carriers at the interface between the substrate and the epitaxial film, and to dry the substrate surface unevenly. The occurrence of can be prevented at the same time.

[Table 1]

Although the GaAs substrate and the InP substrate have been described as examples in the above-mentioned embodiments, the present invention is not limited to this, and the substrate and the epitaxial layer are formed due to the cleaning and drying of the substrate. Other compound semiconductor substrates (for example, III-V group compounds, II) in which electrically active carriers may accumulate at the interface with the film or uneven drying may occur.
It is also applicable to the production of a group VI compound or a compound having a mixed crystal composition of ternary or more). Board size and thickness,
The orientation of the main surface, the crystal growth method, etc. are shown as examples, and are not limited in any way.

In addition to hydrogen peroxide as an oxidant,
Nitric acid, ozone, etc. may be used, or the substrate surface may be oxidized by thermal oxidation or natural oxidation instead of using an oxidizing agent. As the oxide removing agent, an aqueous solution of sodium hydroxide, hydrochloric acid or hydrofluoric acid may be used in addition to aqueous ammonia and phosphoric acid.

Further, in manufacturing the GaAs substrate,
The concentration of H ₂ O ₂ is not limited to 0.1% and may be 0.01 to 5%, preferably 0.05 to 0.3%. The reason is that when the H ₂ O ₂ concentration exceeds 5%, clouding may occur on the substrate surface, while when it is less than 0.01%, uneven drying may occur.

Needless to say, the time for immersing the substrate in each of the solutions of Examples 1 to 4 is not limited to the time exemplified in the above Examples.

[0045]

According to the method of manufacturing a compound semiconductor substrate according to the present invention, spin drying is performed by once covering the surface of the substrate with an oxide film and then removing the oxide film after cleaning the substrate and before drying. Not only the method but also other drying methods can simultaneously prevent the accumulation of electrically active carriers and the occurrence of drying unevenness at the interface between the substrate and the epitaxial film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Fukui 3-17-35, Shinzonan, Toda City, Saitama Prefecture Within Japan Energy Co., Ltd.

Claims (3)

[Claims] 1. A method of cleaning a thin plate-like substrate made of a compound semiconductor, oxidizing the substrate to cover the surface of the substrate with an oxide film, removing the oxide film, and then drying the substrate. And a method for manufacturing a compound semiconductor substrate. 2. The method for producing a compound semiconductor substrate according to claim 1, wherein the oxide film is removed by immersing the substrate covered with the oxide film in an oxide removing agent having no oxidizing power. . 3. The method for manufacturing a compound semiconductor substrate according to claim 2, wherein the oxide removing agent is ammonia water, an aqueous sodium hydroxide solution, phosphoric acid, hydrochloric acid or hydrofluoric acid.