JP2002043270A - Cleaning method for gallium nitride based compound semiconductor growth substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a hydrocarbon from firmly adhering to a substrate surface by organic cleaning, or to efficiently remove even if a hydrocarbon adheres to a substrate surface. The purpose is to provide. SOLUTION: In organic cleaning of a substrate, all organic solvents used are maintained at a temperature lower than the boiling point, thereby preventing hydrocarbons in the organic solvent from firmly adhering to the substrate surface. Further, after the substrate is organically washed, the substrate is further washed with an acid or alkali, or with ultraviolet ozone, so that the hydrocarbon adhering to the substrate surface is effectively removed. Further, by using an acid or an alkali instead of an organic solvent for cleaning the substrate, the adhesion of the hydrocarbon to the substrate surface is prevented.

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 gallium nitride-based compound semiconductor growth substrate used for a light emitting device such as a light emitting diode or a semiconductor laser.

[0002]

2. Description of the Related Art Gallium nitride-based compound semiconductors are used as semiconductor materials for short-wavelength light-emitting devices such as light-emitting diodes and semiconductor lasers.
A structure in which a gallium nitride-based compound semiconductor thin film is laminated on a substrate is used.

A substrate used for a gallium nitride-based compound semiconductor is generally sapphire.
C, GaN, ZnO, GaAs and the like are available. In order to form a high-quality gallium nitride-based compound semiconductor thin film on these substrates, it is necessary to remove impurities such as organic substances attached to the substrate surface in advance. Therefore, the substrate is generally cleaned.

A cleaning method for removing organic substances on the substrate surface is described in, for example, P371 of “Surface Physical Properties Handbook”.
Posted in Here, a method of treating the substrate surface with an organic solvent that dissolves contaminating organic substances or a solubilizing surfactant solution (a nonionic type that does not contain an alkali metal), or oxidizing and decomposing organic substances with an oxidizing agent or the like is used. The method of volatilization is introduced, and a high cleaning effect of the substrate surface is obtained.

In general, an organic solvent which is easily available and has a high organic substance removing effect is used for organic cleaning of a substrate in a semiconductor manufacturing process. A substrate surface can be obtained. The types of the organic solvent for cleaning the substrate are listed in, for example, a list of P108 to P109 of “Optimal precision cleaning technology”. In general, solvent naphtha,
Organic solvents such as acetone, methanol, ethanol, and isopropyl alcohol are often used in combination.
These organic solvents are generally used in order from those having low hydrophilicity to those having high hydrophilicity. For example, organic washing is performed in the order of solvent naphtha, acetone, and methanol.

[0006] A boiled organic solvent is generally used for such organic cleaning of the substrate. By boiling the organic solvent, the effect of removing organic substances on the substrate surface can be enhanced or the substrate can be dried evenly. It can be carried out.

[0007]

By using the above-described organic cleaning method for a substrate, a light-emitting device comprising most compound semiconductors other than the gallium nitride-based compound semiconductor has been manufactured without any problem.

However, as described above, when a substrate is washed or dried by boiling an organic solvent, the characteristics of the light-emitting device made of a gallium nitride-based compound semiconductor are greatly reduced. There is.

For example, when cleaning a substrate with an organic solvent,
When a GaN substrate A in which an organic solvent is boiled and a GaN substrate B in which an organic solvent is not boiled are prepared, and light emitting elements made of a gallium nitride-based compound semiconductor are formed on these substrates under the same conditions, The light output of the light emitting device manufactured on the GaN substrate A was reduced to less than half that of the light emitting device manufactured on the GaN substrate B.

[0010] In addition to the GaN substrate, a light emitting element made of a gallium nitride-based compound semiconductor using a sapphire substrate or a SiC substrate also has a similar degree of reduction in light emitting characteristics, although the degree is different.

[0011] The decrease in the light emission characteristics of such a light emitting element is as follows.
By washing and drying the substrate by boiling the organic solvent as in the conventional case, the hydrocarbon in the organic solvent adheres to the substrate surface, and this hydrocarbon forms some kind of gallium nitride-based compound semiconductor on the substrate. It is presumed to have been caused by the influence.

Such an example has not been reported for a light emitting device made of another compound semiconductor, and is considered to be a problem peculiar to a gallium nitride-based compound semiconductor.

By the way, at the time of organic cleaning of the substrate, at least the hydrocarbon (CmHn) contained in the organic solvent is used.
And impurities such as moisture adhere to the substrate surface and remain on the substrate surface even after the substrate is dried. At the same time, an oxide film is formed on the substrate surface by oxygen in the air. Therefore, in order to obtain a clean substrate surface, before laminating a compound semiconductor thin film on the substrate after organic cleaning, the substrate is heated at a high temperature in a thin film growth apparatus to remove impurities such as moisture and an oxide film. Cleaning is generally performed.

When a substrate such as sapphire or SiC is used, the thermal cleaning is performed at a high temperature of about 1000 ° C. in an atmosphere of hydrogen and nitrogen. In this thermal cleaning, as the concentration of hydrogen in the atmosphere increases, the effect of removing impurities and oxide films increases, but hydrocarbons that adhere to the substrate surface due to boiling of the organic solvent adhere strongly to the surface, It is considered that thermal cleaning does not completely remove the residual and remains on the substrate surface.

In particular, when a light emitting device made of a gallium nitride-based compound semiconductor is manufactured on a substrate made of a gallium nitride-based compound semiconductor, the influence of such hydrocarbons on the surface of the substrate tends to appear strongly. .

In the case of a substrate made of a gallium nitride-based compound semiconductor, if the concentration of hydrogen in the atmosphere is increased in thermal cleaning to enhance the effect of removing impurities and oxide films, nitrogen is desorbed from the substrate surface. In some cases, the removal of hydrocarbons from the substrate surface by thermal cleaning cannot be effectively performed due to degradation of crystallinity.

Accordingly, the present invention provides a method of cleaning a substrate, which prevents hydrocarbons from firmly adhering to the substrate surface,
Alternatively, by providing a method for cleaning a substrate that removes most of hydrocarbons even when the hydrocarbons adhere to the substrate surface, it is possible to manufacture a light-emitting element composed of a gallium nitride-based compound semiconductor thin film without deterioration in light-emitting characteristics. And

[0018]

In order to solve the above-mentioned problems, the present invention provides a method for cleaning a substrate for growing a gallium nitride-based compound semiconductor, wherein all organic solvents used are brought to a temperature lower than their boiling points (preferably room temperature). ), And a step of performing an organic cleaning while maintaining the temperature. With this configuration,
It is possible to provide a method for cleaning a gallium nitride-based compound semiconductor growth substrate, which prevents hydrocarbons in an organic solvent from firmly adhering to the substrate surface.

The present invention also relates to a method for cleaning a substrate for growing a gallium nitride compound semiconductor, wherein an acid cleaning step of cleaning the substrate using an acidic solution, an alkali cleaning step of cleaning the substrate using an alkaline solution, or It has a configuration including an ultraviolet ozone cleaning step of cleaning the substrate with ultraviolet ozone. With this configuration, hydrocarbons adhering to the substrate surface or adhering to the substrate surface during washing with an organic solvent are oxidatively decomposed by an acid, alkali, or ultraviolet ozone to reduce contamination of the substrate surface by the hydrocarbon. Can be.

[0020]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 is a method for cleaning a substrate for growing a gallium nitride-based compound semiconductor, comprising an organic cleaning step of cleaning the substrate using an organic solvent maintained at a temperature lower than the boiling point. Yes, it has the effect of effectively removing contaminants such as organic substances on the substrate surface in washing with an organic solvent, and also preventing the strong attachment of hydrocarbons to the substrate surface by the organic solvent itself in the organic washing step. .

According to a second aspect of the present invention, there is provided a method for growing a gallium nitride-based compound semiconductor, comprising an acid washing step of washing a substrate using an acidic solution and / or an alkali washing step of washing a substrate using an alkaline solution. This is a method for cleaning a substrate, and has an effect that hydrocarbons adhering to a substrate surface can be removed by acid cleaning and / or alkali cleaning.

According to a third aspect of the present invention, there is provided a method of cleaning a substrate for growing a gallium nitride-based compound semiconductor, the method comprising a step of cleaning the substrate with ultraviolet ozone. It has the effect of being able to be removed by ozone cleaning.

According to a fourth aspect of the present invention, there is provided an organic cleaning step of cleaning the substrate using an organic solvent, and after the organic cleaning step, an acid cleaning step of cleaning the substrate with an acidic solution and / or cleaning of the substrate with an alkaline solution. A method of cleaning a substrate for growing a gallium nitride-based compound semiconductor, comprising: an alkali cleaning step of cleaning; a method of effectively removing contaminants such as organic substances on the substrate surface in the cleaning with an organic solvent; Hydrocarbons that have adhered to the substrate surface by themselves can be removed by acid washing and / or alkali washing.

According to a fifth aspect of the present invention, there is provided a gallium nitride comprising: an organic washing step of washing a substrate using an organic solvent; and an ultraviolet ozone washing step of washing the substrate with ultraviolet ozone after the organic washing step. This is a method for cleaning a substrate for growing a compound semiconductor, which can effectively remove contaminants such as organic substances on the substrate surface by cleaning with an organic solvent, and removes hydrocarbons adhered to the substrate surface by the organic solvent itself in the organic cleaning step with ultraviolet rays. It has the effect of being able to be removed by ozone cleaning.

According to a sixth aspect of the present invention, the organic cleaning step is an organic cleaning step of cleaning the substrate using an organic solvent maintained at a temperature lower than the boiling point. The method for cleaning a substrate for growing a gallium nitride-based compound semiconductor described in (1), which can effectively remove contaminants such as organic substances on the substrate surface by cleaning with an organic solvent, and adhere to the substrate surface by the organic solvent itself in the organic cleaning step. It has the effect that the hydrocarbons thus removed can be removed by acid washing, alkali washing, or ultraviolet ozone washing.

According to a seventh aspect of the present invention, there is provided a pure water washing step of washing the substrate with pure water.
7. The method for cleaning a gallium nitride-based compound semiconductor growth substrate according to any one of items 1 to 6, wherein the method has a function of cleaning hydrocarbons, organic solvents, acidic solutions, and alkaline solutions attached to the substrate surface. .

The invention according to claim 8 is the gallium nitride-based compound semiconductor according to any one of claims 1 to 7, wherein the surface of the gallium nitride-based compound semiconductor growth substrate is made of a gallium nitride-based compound semiconductor. This is a method of cleaning a substrate for growing a compound semiconductor, in which the surface of a substrate made of a gallium nitride-based compound semiconductor is susceptible to a hydrocarbon for a light emitting device made of a gallium nitride-based compound semiconductor. Has the effect of preventing contamination by the

The method for cleaning a gallium nitride-based compound semiconductor growth substrate of the present invention will be described below with reference to the drawings.

FIG. 1A is a flowchart of the substrate cleaning step according to the first embodiment of the present invention, and FIG. 1B is a flowchart of the substrate cleaning step according to the second embodiment of the present invention. -Char-
FIG. 1C is a flowchart of a substrate cleaning step according to the third embodiment of the present invention, and FIG. 1D is a flowchart of a substrate cleaning step according to the fourth embodiment of the present invention. Chart.

(Embodiment 1) In Embodiment 1 of the present invention, as shown in the flowchart of FIG. 1 (A), an organic solvent maintained at a temperature lower than the boiling point (preferably room temperature) is used. After the substrate is immersed in the substrate, cleaning by ultrasonic irradiation (hereinafter, abbreviated as "ultrasonic cleaning") is performed, and then the organic solvent on the substrate surface is dried and removed by nitrogen blowing.

According to this method, since the substrate is not boiled during the organic washing and drying steps of the substrate, it is possible to prevent the hydrocarbon from firmly adhering to the substrate surface, and to remove most of the hydrocarbon on the substrate surface. Can be removed.

(Embodiment 2) In Embodiment 2 of the present invention, as shown in the flowchart of FIG. 1B, ultrasonic cleaning is performed with the substrate immersed in an organic solvent. After
The organic solvent on the substrate surface is dried and removed by nitrogen blowing.

Next, after washing with alkali, the alkali adhering to the substrate surface is replaced and removed by ultrasonic cleaning in overflow of pure water, and moisture on the substrate surface is dried and removed by nitrogen blowing.

Subsequently, after cleaning with an acid, the acid adhering to the substrate surface is replaced and removed by ultrasonic cleaning in flowing pure water. Finally, moisture on the substrate surface is dried and removed by nitrogen blowing.

According to this method, the hydrocarbon which still adheres to the substrate surface after the organic cleaning can be decomposed and removed by the oxidative decomposition action of an acid or an alkali.

Concentrated sulfuric acid, nitric acid, hydrochloric acid and the like can be used as the acid, and an aqueous solution of ammonium hydrogen peroxide, potassium hydroxide, sodium hydroxide and the like can be used as the alkali.

As the washing procedure, the acid washing and the alkali washing may be reversed, and the effect of removing the hydrocarbon adhering to the substrate surface can be obtained by washing only one of the acid and the alkali.

Embodiment 3 In Embodiment 3 of the present invention, as shown in the flowchart of FIG. 1C, ultrasonic cleaning is performed while the substrate is immersed in an organic solvent. After
The organic solvent on the substrate surface is dried and removed by nitrogen blowing. Subsequently, the hydrocarbon on the substrate surface is removed by an ultraviolet ozone method.

In this method, after the organic cleaning, the substrate surface is still
Hydrocarbon attached to the surface is generated by decomposition of ozone
By reacting with the generated radical oxygen, CO,
CO _Two, H_TwoIt can be oxidatively decomposed into O and removed.

Here, as contents common to the first to third embodiments, the organic solvent used for the organic cleaning includes solvent naphtha, acetone, alcohol (isopropyl alcohol, ethanol, methanol, etc.) and the like. Although it is used, as described above, it is desirable to sequentially wash the organic solvent with low hydrophilicity (such as solvent naphtha) to the organic solvent with high hydrophilicity (such as alcohol).

In the organic cleaning, a spray cleaning method in which an organic solvent is poured onto a substrate by a nozzle or the like to perform cleaning may be used in addition to a method of immersing the substrate in an organic solvent and performing ultrasonic cleaning.

Further, by performing pure water cleaning immediately after the organic cleaning, there is an effect of preventing hydrocarbons from adhering to the substrate surface due to the organic solvent itself.

The cleaning with pure water can be performed after the substrate is once dried after the organic cleaning. However, it is preferable to replace the organic solvent with pure water immediately after the organic cleaning.

(Embodiment 4) In Embodiment 4 of the present invention, as shown in the flowchart of FIG.
In the step (B), washing with an organic solvent is not performed.

First, after cleaning with alkali, the alkali adhering to the substrate surface is replaced and removed by ultrasonic cleaning in overflow of pure water. Subsequently, after cleaning with an acid, the acid adhering to the substrate surface is replaced and removed by ultrasonic cleaning in pure water overflow. Finally, moisture on the substrate surface is dried and removed by nitrogen blowing.

This is an effective cleaning method when a substrate having a low surface contamination level is used. Hydrocarbons and the like adhering to the substrate surface can be decomposed and removed by oxidative decomposition by an acid or alkali. . Further, since no organic solvent is used, it is possible to prevent hydrocarbon from adhering to the substrate surface due to the organic solvent itself, and to obtain an excellent cleaning effect.

Concentrated sulfuric acid, nitric acid, hydrochloric acid and the like for the acid, ammonia hydrogen peroxide and potassium hydroxide for the alkali,
Sodium hydroxide or the like can be used.

As the cleaning procedure, the acid cleaning and the alkali cleaning may be reversed, or even if only one of the acid and the alkali is cleaned, the effect of removing the hydrocarbon adhering to the substrate surface can be obtained.

Here, as a content common to the first to fourth embodiments, the drying of the substrate is performed by a method other than the method using nitrogen blowing.
It may be blown with another clean gas, or may be performed by a method such as spin drying, hot air circulation drying, or infrared lamp heating drying.

The substrate is made of sapphire, SiC, GaAs,
In addition to a substrate such as ZnO, the cleaning methods of Embodiments 1 to 4 are used for a substrate whose surface is made of a gallium nitride-based compound semiconductor (such as a substrate in which a gallium nitride-based compound semiconductor is stacked on a sapphire substrate). be able to. In particular, the light-emitting characteristics of a light-emitting element made of a gallium nitride-based compound semiconductor manufactured on a substrate made of a gallium nitride-based compound semiconductor are easily affected by hydrocarbons attached to the substrate surface.

Therefore, by applying the cleaning method of the present invention, the adhesion of hydrocarbons to the substrate surface can be suppressed or prevented. Therefore, the gallium nitride-based compound semiconductor formed on the substrate whose surface is made of a gallium nitride-based compound semiconductor can be used. It is possible to prevent a decrease in light emission characteristics of the light emitting element.

[0052]

Embodiment 1 Embodiment 1 of the present invention will be described below with reference to FIG.

FIG. 2 is a sectional view showing a layer structure of a gallium nitride-based compound semiconductor to which the method for cleaning a substrate according to Examples 1 to 4 of the present invention and Comparative Example 1 is applied.

Using a MOCVD apparatus, GaN was laminated on a sapphire substrate at a thickness of 1 μm (a 2-inch φ wafer was divided into two equal parts) and used as a substrate 1 for cleaning.

First, a 500 cc beaker (manufactured by Pyrex (registered trademark)) used for cleaning was sufficiently cleaned with hydrofluoric acid, and the substrate 1 was placed vertically on a hanger.

Next, solvent naphtha, acetone and isopropyl alcohol were added to the three beakers (A to C) for 3 times each.
I put in 00cc each. However, all the organic solvents in the above three beakers are used at room temperature.

The hanger on which the substrate 1 was placed was immersed in a beaker A containing solvent naphtha, and was subjected to ultrasonic cleaning for 10 minutes. Next, the hanger was immersed in the beaker B containing acetone, and similarly ultrasonically cleaned for 10 minutes. Further, the hanger was immersed in a beaker C containing isopropyl alcohol, and was similarly subjected to ultrasonic cleaning for 10 minutes.

Subsequently, isopropyl alcohol was replaced with pure water by performing ultrasonic cleaning for 10 minutes in pure water overflow.

Thereafter, the substrate was placed on the filter paper with tweezers, nitrogen was blown from the center of the substrate 1 using a nitrogen gun, and water on the surface of the substrate 1 was blown off to the periphery of the substrate 1 and dried and removed.

Then, the cleaned substrate 1 is subjected to MOCVD.
It was placed in the reactor of the apparatus.

First, the temperature of the substrate 1 was raised from room temperature to 1050 ° C. while flowing nitrogen at 4 L / min, hydrogen at 4 L / min, and ammonia at 2 L / min. While holding, contaminants such as organic substances and water remaining on the surface of the substrate 1 were removed.

Next, while flowing nitrogen and hydrogen at 13 L / min and 3 L / min, respectively, ammonia was supplied at 4 L / min and TMG at 80 μmol / min, and GaN was supplied.
Layer 2 was grown to a thickness of 0.2 μm.

Next, the supply of TMG was stopped and the substrate temperature was lowered to 7 ° C.
At 700 ° C. and nitrogen at 14 ° C.
6 l / min ammonia while flowing at l / min
Min, TMG 4 μmol / min, TMI 1 μmol / min
Then, a well layer 3 having a single quantum well structure made of undoped In _0.2 Ga _0.8 N was grown to a thickness of 2 nm.

After the growth of the well layer, the supply of TMI is stopped.
While flowing nitrogen at 14 liters / minute, TMG was
The GaN layer 4 was grown to a thickness of 4 nm while raising the substrate temperature to 1050 ° C., and when the substrate temperature reached 1050 ° C., nitrogen and hydrogen were respectively supplied. While flowing at 13 liters / minute and 3 liters / minute, 4 liters / minute of ammonia and 80 μmo of TMG
The top layer 5 of GaN was grown to a thickness of 100 nm at a rate of 1 / min. The nitride semiconductor thus obtained was used as Sample 1.

(Comparative Example 1) MOC was used as a substrate for cleaning.
Using a VD device, GaN was 1 μm on a sapphire substrate
A laminated product (the other of the substrates obtained by bisecting the 2-inch φ wafer used in Example 1) was used.

Further, a 500 cc beaker D was added (for boiling isopropyl alcohol) to make a total of four beakers.

First, ultrasonic cleaning was sequentially performed for 10 minutes with solvent naphtha, acetone, and isopropyl alcohol (all at normal temperature) in the same procedure as in Example 1. Also, add 300 c of isopropyl alcohol to beaker D in advance.
c, and boil with a hot plate.

After ultrasonic cleaning of isopropyl alcohol at room temperature, a bead containing boiled isopropyl alcohol was added.
The hanger was immersed in Car D and heated for 5 minutes. After the heating, the hanger was immediately pulled up so that the boiling bubbles did not come into contact with the substrate surface, and the substrate was taken out with tweezers. The substrate surface was already dry when pulled up.

The substrate 1 thus cleaned was placed on the reaction tube of the MOCVD apparatus at the same time as the substrate of Example 1, and the growth described in Example 1 was performed. did.

The PL intensity of Sample 1 of Example 1 and Sample 2 of Comparative Example 1 were compared using a photoluminescence (PL) measuring device. The excitation light used in the PL measuring apparatus was a He-Cd laser (wavelength: 325 nm), and the excitation intensity was 10 mW.

As a result, the PL intensity of sample 1
Approximately 20 times the strength was obtained as compared to the L strength. this is,
In the organic cleaning of the substrate, it is clearly shown whether isopropyl alcohol is boiled or not. By not boiling isopropyl alcohol, the adhesion of hydrocarbon to the substrate surface can be suppressed. The light emitting characteristics of the gallium nitride-based compound semiconductor having the InGaN well layer grown on the substrate could be improved.

In Comparative Example 1, isopropyl alcohol was boiled. However, it was confirmed that the PL intensity of the gallium nitride-based compound semiconductor was also reduced by boiling with acetone, ethanol, and methanol.

(Embodiment 2) As in Embodiment 1, the MOCV
Using a D apparatus, a GaN layer of 1 μm was laminated on a sapphire substrate and used as a cleaning substrate 6.

The total number of 500 cc beakers A to G used in this washing is seven. The same beakers A to D as those in Comparative Example 1 were prepared.

First, after washing and drying the substrate as in Comparative Example 1, 300 cc of an aqueous solution of ammonia hydrogen peroxide (NH ₃ : H ₂ O ₂ : H ₂ O = 1: 1: 5) at room temperature was introduced. The hanger was immersed in the beaker E, stirred for 5 minutes, and then subjected to ultrasonic cleaning in pure water overflow. Then, the substrate surface was dried by nitrogen blowing.

Next, the hanger is immersed in a beaker F containing 300 cc of concentrated sulfuric acid (maintained at 60 ° C. on a hot plate), stirred for 5 minutes, and then overflowed in a pure water overflow using a beaker G filled with pure water. Was subjected to ultrasonic cleaning. Then, the substrate surface was dried by nitrogen blowing.

The substrate thus cleaned was used to form the same nitride semiconductor by the same growth method as in Example 1 to obtain Sample 3.

When the PL intensity of the sample 3 was measured, it was 60% of the PL intensity of the sample 1.
Of the sample 1 was 5% of that of the sample 1, which was greatly improved.

From this, most of the hydrocarbons firmly adhered to the substrate surface by performing boiling of the organic solvent (isopropyl alcohol in this example) in cleaning and drying the substrate are removed by performing alkali cleaning and acid cleaning. We were able to.

(Embodiment 3) As in Embodiment 1, MOCV
Using a D apparatus, a GaN layer having a thickness of 1 μm laminated on a sapphire substrate was used as a substrate 1 for cleaning.

In this example, after the same substrate cleaning and substrate drying as in Comparative Example 1 were performed, ultraviolet ozone cleaning was performed for 5 minutes using an ultraviolet irradiation device having an ozone generator.

The same nitride semiconductor was produced from the substrate washed in the same manner as in Example 1 by using the same growth method as in Example 1 to obtain Sample 4.

When the PL intensity of the sample 4 was measured, it was 80% of the PL intensity of the sample 1, and a further improvement was obtained.

Thus, even if hydrocarbons firmly adhered to the substrate surface by boiling an organic solvent (isopropyl alcohol in this example) in washing and drying the substrate, much of the hydrocarbons were removed by ultraviolet ozone washing. We were able to.

(Embodiment 4) As in Embodiment 1, MOCV
Using a D apparatus, GaN having a thickness of 1 μm laminated on a sapphire substrate was used as a cleaning substrate.

In this example, a cleaning method in which the organic cleaning of the substrate (immersion in solvent naphtha to drying by boiling in isopropyl alcohol) in the cleaning method in Example 2 was omitted.

The substrate washed in this manner was used as a sample 5 by producing the same nitride semiconductor by the same growth method as in the first embodiment.

When the PL intensity of the sample 5 was measured, an intensity equivalent to the PL intensity of the sample 1 was obtained.

Thus, by not performing organic cleaning, it is possible to prevent hydrocarbons of the organic solvent itself from adhering to the substrate surface, and by performing alkali cleaning and acid cleaning, it is possible to prevent organic substances and the like that have adhered before cleaning. Most of the contaminants could be removed.

When a large amount of organic substances adhere to the substrate surface before cleaning, organic cleaning is performed before alkali cleaning and acid cleaning as in Example 2 to further enhance the cleaning effect. It is desirable.

Embodiment 5 A method for manufacturing a light emitting device using a gallium nitride-based compound semiconductor according to a second embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a sectional view showing a layer structure of a gallium nitride-based compound semiconductor light emitting device to which the method for cleaning a substrate according to the second embodiment of the present invention is applied.

After GaN having a thickness of 120 μm is laminated on a sapphire substrate by HVPE (hydride vapor phase epitaxy), a diamond slurry (abrasive grains) having a depth of 10 μm is used to remove irregularities on the substrate surface. Polishing was performed. After polishing, organic substances and impurities such as lubricating oil and wax at the time of polishing were removed by organic washing, and then a damaged layer generated on the GaN surface by machining was removed by a reactive ion etching method. Thus, the surface is GaN
Was formed.

The substrate placed vertically was placed on a hanger, and seven beakers (A to G) of 500 cc sufficiently washed with hydrofluoric acid (A to G) were prepared. Solvent naphtha, acetone and isopropyl alcohol were placed in the beakers A to C. 300 cc each. However, the above three beakers
All the organic solvents in are used at normal temperature.

First, the hanger on which the substrate 6 was placed was immersed in a beaker A containing solvent naphtha, and was subjected to ultrasonic cleaning for 10 minutes. Next, beaker B containing acetone
The hanger was immersed in the inside, and ultrasonic cleaning was similarly performed for 10 minutes. Further, the hanger was immersed in a beaker C containing isopropyl alcohol, and was similarly subjected to ultrasonic cleaning for 10 minutes.

Subsequently, isopropyl alcohol was replaced with pure water by performing ultrasonic cleaning for 10 minutes in pure water overflow.

Thereafter, the substrate 6 was placed on filter paper with tweezers, nitrogen was blown from the center of the substrate using a nitrogen gun, and water on the substrate surface was blown off to the periphery of the substrate and dried and removed.

Next, ammonia, hydrogen peroxide and water were mixed in a ratio of 1:
A hanger was placed in a beaker D containing 300 cc of an alkaline aqueous solution mixed at a ratio of 1: 5, and the mixture was stirred for 5 minutes.
After transferring the hanger to the beaker E containing pure water and performing ultrasonic cleaning for 10 minutes while overflowing the pure water,
The substrate 6 was placed on the filter paper with tweezers, nitrogen was blown from the center of the substrate 6 using a nitrogen gun, and water on the substrate surface was blown off to the periphery of the substrate and dried.

Next, the hanger was transferred to a beaker F containing 300 cc of concentrated sulfuric acid kept at 60 ° C. on a hot plate, washed with acid for 5 minutes, and then transferred to a beaker G containing pure water. Ultrasonic cleaning was performed for 10 minutes while overflowing water. Subsequently, the substrate was placed on filter paper with tweezers, nitrogen was blown from the center of the substrate using a nitrogen gun, moisture on the substrate surface was blown off to the periphery of the substrate, and the substrate was dried.

The substrate 6 thus cleaned is subjected to MOCV
It was placed on a substrate holder in a reaction tube of the D apparatus.

First, the temperature of the substrate 6 was raised from room temperature to 1050 ° C. while flowing nitrogen at 4 L / min, hydrogen at 4 L / min, and ammonia at 2 L / min. Thus, dirt and moisture such as organic substances remaining on the surface of the substrate 6 were removed.

Thereafter, the temperature of the substrate 6 was maintained at 1050 ° C., and ammonia was supplied at a flow rate of 13 l / min and 3 l / min as carrier gases while supplying ammonia at 4 l / min.
Liter / min, TMG 80 μmol / min, 10 ppm
Diluted SiH ₄ is supplied at 10 cc / min. To make the first n-type clad layer 7 made of GaN doped with Si 2 μm.
m.

After growing the first n-type cladding layer 7, the substrate 6
At a temperature of 1050 ° C., while flowing nitrogen and hydrogen as carrier gases at 15 liters / minute and 3 liters / minute, respectively, ammonia at 2 liters / minute and TMG at 40 μm.
The second n-type cladding layer 8 made of undoped Al _0.05 Ga _0.95 N was grown to a thickness of 20 nm by supplying ol / min and TMA at 3 μmol / min.

After growing the second n-type cladding layer 8, TMG
And supply of SiH ₄ were stopped, the substrate temperature was lowered to 700 ° C., and at 700 ° C., nitrogen was flowed at 14 liters / minute as a carrier gas, while 6 liters / minute of ammonia, 4 μmol / minute of TMG, and TMI 1 μmol
The light emitting layer 9 having a single quantum well structure made of undoped In _0.15 Ga _0.85 N was grown to a thickness of 2 nm.

After the light emitting layer 9 is grown, the supply of TMI is stopped.
While supplying nitrogen as carrier gas at 14 L / min, ammonia at 6 L / min, and TMG at 2 μmol / min, while increasing the temperature of the substrate 6 toward 1050 ° C., the intermediate layer made of undoped GaN is continuously formed. 10 was grown to a thickness of 4 nm.

After the formation of the intermediate layer 10, the temperature of the substrate 6 is set to 1
While maintaining the temperature at 050 ° C. and continuously flowing nitrogen and hydrogen as carrier gases at 15 liters / minute and 3 liters / minute, respectively, ammonia was supplied at 2 liters / minute, and TMG was supplied at 40 μm.
ol / min, TMA 3 μmol / min, Cp ₂ Mg 0.
Mg-doped Al supplied at 4 μmol / min.
_The p-type cladding layer 11 made of _0.05 Ga _0.95 N
m.

After growing the p-type cladding layer 11, TMG and T
The supply of MA and Cp ₂ Mg was stopped, and nitrogen was reduced to 18 liters /
Then, while flowing ammonia at a rate of 2 liters / minute, the temperature of the substrate 6 was cooled to about room temperature, and a wafer having the gallium nitride-based compound semiconductor laminated on the substrate 6 was taken out of the reaction tube.

Incidentally, TMG which is an organometallic compound, TM
I, TMA, and Cp ₂ Mg were all supplied to the reaction tube by being vaporized by a hydrogen carrier gas.

The laminated structure made of the gallium nitride-based compound semiconductor thus formed was not subjected to separate annealing, and nickel (Ni) and gold (Au) were each deposited on the surface by vapor deposition to a thickness of 5 nm. Then, the light transmitting electrode 12 was formed by photolithography and wet etching.

Thereafter, an insulating film (not shown) made of SiO ₂ is deposited to a thickness of 0.5 μm on the light transmitting electrode 12 and the exposed p-type cladding layer 11 by the CVD method. And the p-type cladding layer 1 while covering the light-transmitting electrode 12 by reactive ion etching.
A mask made of an insulating film exposing a part of the surface of Sample No. 1 was formed.

Next, the p-type cladding layer 11 is exposed from the exposed surface of the p-type cladding layer 11 by a reactive ion etching method using a chlorine-based gas using the above mask.
, The intermediate layer 10, the light emitting layer 9, and the second n-type cladding layer 8 are removed at a depth of about 0.4 μm, and the first n-type cladding layer 7 is removed.
Surface was exposed.

After the above steps, the insulating film is once removed by wet etching, and a part of the surface of the light transmitting electrode 12 and the exposed first n are removed by vapor deposition and photolithography. 0.1 μm thick titanium (Ti) and 0.5 μm thick A
u were laminated to form an n-side electrode 13 and a p-side electrode 14, respectively. After that, the surface of the light transmitting electrode 12 is coated with 0.2 μm by plasma CVD and photolithography.
An m-thick insulating film (not shown) made of SiO ₂ was formed.

Thereafter, sapphire and GaN were further polished and removed from the rear surface of the substrate 6 to a thickness of about 10 μm to form a wafer having a thickness of about 100 μm, which was separated into chips by scribing.

After this chip was bonded to the stem with the electrode forming surface facing upward, the p-side electrode 14 and the n-side electrode 13 of the chip were connected to the respective electrodes on the stem with wires, and then resin-molded to form a light emitting device. Was prepared as Sample 3.
When this light-emitting device was driven by a forward current of 20 mA, light was emitted in blue with a peak wavelength of 470 nm. At this time, the light emission output was 2.5 mW and the forward operation voltage was 3.5 V, and excellent light emission characteristics could be obtained.

In the above-described embodiment, an example in which the present invention is mainly applied to a light emitting diode has been described. However, the present invention is not limited to a light emitting diode, but is applied to a light emitting device such as a semiconductor laser using a gallium nitride compound semiconductor. It is also possible.

[0116]

According to the present invention, the following effects can be obtained.

In washing and drying with an organic solvent,
Contaminants such as organic substances on the substrate surface can be effectively removed, and since the organic solvent is not boiled, it is possible to prevent strong attachment of hydrocarbons to the substrate surface in the organic cleaning step.

Further, even when hydrocarbons adhere to the substrate surface by organic cleaning, the hydrocarbons adhering to the substrate surface can be efficiently removed by performing acid or alkali cleaning or ultraviolet ozone cleaning. .

Further, by performing acid and alkali cleaning without performing organic cleaning, it is possible to prevent hydrocarbons from adhering to the substrate surface due to the organic solvent itself.

As a result, it is possible to prevent the light emitting output of the light emitting device made of the gallium nitride compound semiconductor fabricated on the cleaned substrate from being reduced.

[Brief description of the drawings]

FIG. 1A is a flowchart of a substrate cleaning step according to a first embodiment of the present invention. FIG. 1B is a flowchart of a substrate cleaning step according to a second embodiment of the present invention. (D) Flowchart of substrate cleaning step according to Embodiment 4 of the present invention (D) Flowchart of substrate cleaning step according to Embodiment 4 of the present invention

FIG. 2 is a cross-sectional view illustrating a layer structure of a gallium nitride-based compound semiconductor to which a method for cleaning a substrate according to Examples 1 to 4 of the present invention and Comparative Example 1 is applied.

FIG. 3 is a cross-sectional view illustrating a layer structure of a gallium nitride-based compound semiconductor light-emitting element to which a method for cleaning a substrate according to a second embodiment of the present invention is applied.

[Explanation of symbols]

 1, 6 substrate 2, 4 GaN layer 3 well layer 5 top layer 7 first n-type clad layer 8 second n-type clad layer 9 light emitting layer 10 intermediate layer 11 p-type clad layer 12 light transmitting electrode 13 n side Electrode 14 p-side electrode

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B08B 7/00 B08B 7/00 (72) Inventor Shuichi Shinagawa 1006 Kazuma, Kazuma, Osaka Matsushita Electric Industrial Co., Ltd. In-house F term (reference) 3B116 AA03 AB01 BB03 BB83 BC01 CC03 CC05 3B201 AA03 AB01 BB04 BB82 BB83 BB89 BB92 BB93 BB95 BB96 BC01 CB15 CC12 CC21

Claims (8)

[Claims] 1. A method of cleaning a substrate for growing a gallium nitride-based compound semiconductor, comprising an organic cleaning step of cleaning the substrate using an organic solvent maintained at a temperature lower than the boiling point. 2. A method for cleaning a substrate for growing a gallium nitride-based compound semiconductor, comprising: an acid cleaning step of cleaning the substrate using an acidic solution; and / or an alkali cleaning step of cleaning the substrate using an alkaline solution. 3. A method for cleaning a substrate for growing a gallium nitride-based compound semiconductor, comprising an ultraviolet ozone cleaning step of cleaning the substrate with ultraviolet ozone. 4. An organic washing step of washing the substrate with an organic solvent, an acid washing step of washing the substrate with an acidic solution and / or an alkali washing step of washing the substrate with an alkaline solution after the organic washing step. A method for cleaning a substrate for growing a gallium nitride-based compound semiconductor, comprising: 5. A gallium nitride based compound semiconductor growth substrate comprising: an organic cleaning step of cleaning a substrate using an organic solvent; and an ultraviolet ozone cleaning step of cleaning the substrate with ultraviolet ozone after the organic cleaning step. Cleaning method. 6. The gallium nitride-based system according to claim 4, wherein said organic cleaning step is an organic cleaning step of cleaning a substrate using an organic solvent maintained at a temperature lower than the boiling point. A method for cleaning a substrate for compound semiconductor growth. 7. The method for cleaning a gallium nitride-based compound semiconductor growth substrate according to claim 1, further comprising a pure water cleaning step of cleaning the substrate with pure water. 8. The cleaning of the gallium nitride-based compound semiconductor growth substrate according to claim 1, wherein a surface of the gallium nitride-based compound semiconductor growth substrate is made of a gallium nitride-based compound semiconductor. Method.