JP4479741B2 - Method for cleaning substrate for growth of gallium nitride compound semiconductor - Google Patents

Description

  The present invention relates to a method for cleaning a gallium nitride-based compound semiconductor growth substrate used for light-emitting elements such as light-emitting diodes and semiconductor lasers.

  Gallium nitride-based compound semiconductors are used as semiconductor materials for short-wavelength light-emitting elements such as light-emitting diodes and semiconductor lasers, and these light-emitting elements usually have a structure in which a gallium nitride-based compound semiconductor thin film is stacked on a substrate. It has been.

  The substrate used for the gallium nitride compound semiconductor is generally sapphire, and other examples include SiC, GaN, ZnO, and GaAs. In order to produce a high-quality gallium nitride compound semiconductor thin film on these substrates, it is necessary to remove impurities such as organic substances adhering to the substrate surface in advance. Therefore, the substrate is generally cleaned.

  A cleaning method for removing organic substances on the surface of the substrate is disclosed in, for example, P371 of “Surface Physical Engineering Handbook”. Here, the organic matter is oxidized and decomposed by a method of treating with an organic solvent that dissolves contaminated organic matter on the substrate surface or a solubilizing surfactant solution (non-ionic type that does not contain alkali metal), or an oxidizing agent. A method of volatilization is introduced, and a high cleaning effect on the substrate surface is obtained.

  In general, organic solvents are used for organic cleaning of substrates in semiconductor manufacturing processes, and organic solvents that are easily available and have a high organic substance removal effect are used. Obtainable. For example, the types of organic solvents for substrate cleaning are listed in the list of P108 to P109 in “Optimum Precision Cleaning Technology”. Generally, solvent naphtha, acetone, methanol, ethanol, isopropyl alcohol, etc. Often combined with organic solvents. These organic solvents are usually used in the order from low hydrophilicity to high hydrophilicity. For example, organic washing is performed in the order of solvent naphtha, acetone, and methanol.

  In such organic cleaning of the substrate, a boiled organic solvent is generally used. By boiling the organic solvent, the effect of removing organic substances on the surface of the substrate can be enhanced or the substrate can be dried uniformly. it can.

  By using the organic cleaning method for a substrate as described above, a light-emitting element made of most compound semiconductors other than the gallium nitride compound semiconductor is produced without any problem.

  However, as described above, when a substrate is cleaned or dried by boiling an organic solvent, the light-emitting element made of a gallium nitride compound semiconductor has a problem that the characteristics of the light-emitting element are significantly deteriorated.

  For example, when a substrate is washed with an organic solvent, a GaN substrate A that has been boiled with an organic solvent and a GaN substrate B that has not been boiled with an organic solvent are prepared, and a gallium nitride compound semiconductor is formed on those substrates. When the light emitting elements to be manufactured under the same conditions, the light output of the light emitting element manufactured on the GaN substrate A was reduced to half or less as compared with the light emitting element manufactured on the GaN substrate B.

  Further, not only the GaN substrate but also the light emitting element made of a gallium nitride compound semiconductor using a sapphire substrate or a SiC substrate, although the degree of difference is similar, the emission characteristics are similarly lowered.

  Such deterioration of the light emitting characteristics of the light emitting element is caused by washing and drying the substrate by boiling the organic solvent as in the past, so that the hydrocarbon in the organic solvent adheres to the substrate surface, and this hydrocarbon is the substrate. This is presumed to have been caused by some influence on the gallium nitride compound semiconductor fabricated on the substrate.

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

  By the way, at the time of organic cleaning of the substrate, impurities such as hydrocarbon (CmHn) and moisture contained in at least the organic solvent 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 the compound semiconductor thin film on the substrate after organic cleaning, the substrate is heated at a high temperature in the thin film growth apparatus, and a thermal for removing impurities such as moisture and oxide films. 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 a hydrogen and nitrogen atmosphere. In this thermal cleaning, the higher the hydrogen concentration in the atmosphere, the higher the effect of removing impurities and oxide films. In particular, hydrocarbons that adhere to the substrate surface due to boiling of the organic solvent are firmly attached to the surface, It is considered that even the thermal cleaning cannot be sufficiently removed and remains on the substrate surface.

  In particular, when a light emitting element made of a gallium nitride compound semiconductor is fabricated on a substrate made of a gallium nitride compound semiconductor, the influence of such contamination of the substrate surface by the hydrocarbon tends to appear strongly.

  In the case of a substrate made of a gallium nitride compound semiconductor, if the hydrogen concentration in the atmosphere is increased in thermal cleaning in order to enhance the effect of removing impurities and oxide films, the crystallinity deterioration due to the desorption of nitrogen from the substrate surface Therefore, there is a situation in which removal of hydrocarbons from the substrate surface by thermal cleaning cannot be performed effectively.

  Therefore, the present invention provides a method for cleaning a substrate that prevents the hydrocarbon from adhering firmly to the substrate surface, or a method for cleaning the substrate that removes most of the hydrocarbon even if it adheres to the substrate surface. It is an object of the present invention to make it possible to manufacture a light-emitting element made of a gallium nitride-based compound semiconductor thin film with no deterioration in light emission characteristics.

  In order to solve the above-mentioned problems, the present invention is a method for cleaning a substrate for growing a gallium nitride compound semiconductor, and performs organic cleaning while maintaining all the organic solvents used at a temperature lower than the boiling point (preferably normal temperature). It consists of the structure provided with the process. With this configuration, it is possible to provide a method for cleaning a gallium nitride-based compound semiconductor growth substrate that prevents the hydrocarbon in the organic solvent from firmly attaching to the substrate surface.

  The present invention also provides a method for cleaning a substrate for growing a gallium nitride compound semiconductor by 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 ultraviolet ozone. It has a configuration including an ultraviolet ozone cleaning process for cleaning the substrate. With this configuration, the hydrocarbon attached to the substrate surface or attached to the substrate surface during cleaning with an organic solvent is oxidized and decomposed with acid, alkali, or ultraviolet ozone to reduce contamination of the substrate surface with hydrocarbon. Can do.

  The following effects can be achieved by the present invention.

  In cleaning 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 adhesion of the hydrocarbon to the substrate surface in the organic cleaning process. .

  Also, even when hydrocarbon is attached to the substrate surface by organic cleaning, the hydrocarbon attached to the substrate surface can be efficiently removed by performing acid or alkali cleaning or ultraviolet ozone cleaning.

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

  Thereby, it is possible to eliminate a decrease in light emission output of a light emitting element made of a gallium nitride compound semiconductor manufactured on a cleaned substrate.

1st invention of this application is the washing | cleaning method of the board | substrate for gallium nitride type compound semiconductor growth provided with the acid washing process which wash | cleans a board | substrate using an acidic solution, and / or the alkali washing process which wash | cleans a board | substrate using an alkaline solution. There is an effect that the hydrocarbon adhering to the substrate surface can be removed by acid cleaning and / or alkali cleaning.

The second invention of the present application is a method for cleaning a substrate for growing a gallium nitride compound semiconductor comprising an ultraviolet ozone cleaning step for cleaning the substrate with ultraviolet ozone, and removes the hydrocarbon adhering to the substrate surface by ultraviolet ozone cleaning. It has the effect of being able to.

The third invention of the present application includes an organic cleaning step of cleaning a substrate using an organic solvent, an acid cleaning step of cleaning the substrate with an acidic solution and / or an alkaline cleaning step of cleaning the substrate with an alkaline solution after the organic cleaning step. And a method for cleaning a substrate for growing a gallium nitride compound semiconductor, which can effectively remove contaminants such as organic substances on the surface of the substrate in the cleaning with the organic solvent, and can be applied to the surface of the substrate by the organic solvent itself in the organic cleaning step. The adhering hydrocarbon can be removed by acid cleaning and / or alkali cleaning.

A fourth invention of the present application is for growing a gallium nitride compound semiconductor, 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. A substrate cleaning method that can effectively remove contaminants such as organic substances on the substrate surface in the cleaning with an organic solvent, and removes the hydrocarbon adhering to the substrate surface by the organic solvent itself in the organic cleaning step by ultraviolet ozone cleaning. It has the effect of being able to.

  Hereinafter, a cleaning method for a gallium nitride compound semiconductor growth substrate of the present invention will be described with reference to the drawings.

  1A is a flowchart of a substrate cleaning process according to Embodiment 1 of the present invention, FIG. 1B is a flowchart of a substrate cleaning process according to Embodiment 2 of the present invention, and FIG. FIG. 1D shows a flowchart of the substrate cleaning process according to the third embodiment of the present invention, and FIG. 1D shows a flowchart of the substrate cleaning process according to the fourth embodiment of the present invention.

(Embodiment 1)
In Embodiment Mode 1 of the present invention, as shown in the flowchart of FIG. 1A, cleaning is performed by ultrasonic irradiation while the substrate is immersed in an organic solvent maintained at a temperature lower than the boiling point (preferably normal temperature). (Hereinafter, abbreviated as “ultrasonic cleaning”), the organic solvent on the substrate surface is removed by drying with nitrogen blowing.

  With this method, the substrate is not boiled in the organic cleaning and drying stages of the substrate, so that it is possible to prevent the hydrocarbon from being firmly attached to the substrate surface and to remove most of the hydrocarbon on the substrate surface. Can do.

(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, and then the organic solvent on the substrate surface is dried by nitrogen blowing. Remove.

  Next, after cleaning with alkali, the alkali adhered to the substrate surface is replaced and removed by ultrasonic cleaning in a pure water overflow, 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 removed by nitrogen blowing.

  In this method, the hydrocarbon still adhering to the substrate surface after organic cleaning can be decomposed and removed by oxidative decomposition action with acid or alkali.

  Further, concentrated sulfuric acid, nitric acid, hydrochloric acid and the like can be used for the acid, and an aqueous solution of ammonia hydrogen peroxide, potassium hydroxide, sodium hydroxide and the like can be used for the alkali.

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

(Embodiment 3)
In Embodiment 3 of the present invention, as shown in the flowchart of FIG. 1 (C), after performing ultrasonic cleaning in a state where the substrate is immersed in an organic solvent, the organic solvent on the surface of the substrate is blown by nitrogen blowing. Remove to dryness. Subsequently, the hydrocarbon on the substrate surface is removed by an ultraviolet ozone method.

In this method, hydrocarbons that still adhere to the substrate surface after organic cleaning can be oxidized and decomposed into CO, CO ₂ , and H ₂ O by reacting with the radical oxygen generated by the decomposition of ozone. it can.

  Here, as contents common to the first to third embodiments, the organic solvent used for organic cleaning is solvent naphtha, acetone, alcohol (isopropyl alcohol, ethanol, methanol, etc.), etc., as described above, It is desirable to perform washing in order from an organic solvent having low hydrophilicity (such as solvent naphtha) to an organic solvent having high hydrophilicity (such as alcohol).

  In addition to the method of ultrasonic cleaning by immersing the substrate in an organic solvent, the organic cleaning can be performed by a spray cleaning method in which the organic solvent is cleaned while being poured onto the substrate with a nozzle or the like.

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

  The pure water cleaning can be performed after the organic cleaning and after the substrate is once dried, but it is preferable that the organic solvent is immediately replaced with pure water after the organic cleaning.

(Embodiment 4)
In Embodiment 4 of the present invention, as shown in the flowchart of FIG. 1D, cleaning with an organic solvent is not performed in the process of FIG.

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

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

  Further, concentrated sulfuric acid, nitric acid, hydrochloric acid and the like can be used for the acid, and ammonia hydrogen peroxide, potassium hydroxide, sodium hydroxide and the like can be used for the alkali.

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

  Here, as contents common to the first to fourth embodiments, the substrate may be dried by a clean gas other than the method using nitrogen blowing, such as spin drying, hot air circulation drying, infrared lamp heating drying. You may carry out by the method by.

  In addition to substrates such as sapphire, SiC, GaAs, ZnO, etc., the substrate is also implemented on a substrate whose surface is made of a gallium nitride compound semiconductor (such as a substrate in which a gallium nitride compound semiconductor is stacked on a sapphire substrate). The cleaning method of Embodiments 1 to 4 can be used. In particular, the light emission characteristics of a light-emitting element made of a gallium nitride-based compound semiconductor manufactured on a substrate whose surface is 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, so that the surface of a gallium nitride compound semiconductor light-emitting device manufactured on a substrate made of a gallium nitride compound semiconductor is used. It is possible to eliminate the deterioration of the light emission characteristics.

Example 1
Hereinafter, Example 1 of the present invention will be described with reference to FIG.

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

  A substrate obtained by laminating 1 μm of GaN on a sapphire substrate (one obtained by dividing a 2-inch φ wafer into two equal parts) was used as a substrate 1 and was used for cleaning.

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

  Next, 300 cc each of solvent naphtha, acetone, and isopropyl alcohol was put into three beakers (A to C). However, all the organic solvents in the three beakers are used at room temperature.

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

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

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

  Then, the cleaned substrate 1 was placed in the reactor of the MOCVD apparatus.

  First, while the temperature of the substrate 1 was raised from room temperature to 1050 ° C. while flowing nitrogen at 4 liters / minute, hydrogen at 4 liters / minute, and ammonia at 2 liters / minute, the temperature was maintained for 2 minutes. Then, contaminants such as organic substances remaining on the surface of the substrate 1 and moisture were removed.

  Next, while supplying nitrogen and hydrogen at 13 liters / minute and 3 liters / minute respectively, ammonia is supplied at 4 liters / minute and TMG is supplied at 80 μmol / minute, and the GaN layer 2 is grown to a thickness of 0.2 μm. I let you.

Next, the supply of TMG is stopped and the substrate temperature is lowered to 700 ° C. At 700 ° C., while flowing nitrogen at 14 liter / min, ammonia is 6 liter / min, TMG is 4 μmol / min, and TMI is 1 μmol / min. The 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 well layer is grown, the supply of TMI is stopped, TMG is supplied at 2 μmol / min while flowing nitrogen at 14 liters / min, and the substrate temperature is raised toward 1050 ° C., and the undoped GaN layer 4 When the substrate temperature reaches 1050 ° C., nitrogen and hydrogen are allowed to flow at 13 liters / minute and 3 liters / minute respectively, while ammonia is 4 liters / minute and TMG is 80 μmol / minute. The top layer 5 of GaN was grown to a thickness of 100 nm. The nitride semiconductor thus obtained was designated as Sample 1.

(Comparative Example 1)
As a cleaning substrate, a MOCVD apparatus was used and 1 μm of GaN was stacked on a sapphire substrate (the other of the two-inch φ wafers used in Example 1 divided into two equal parts).

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

  First, in the same procedure as in Example 1, ultrasonic cleaning was sequentially performed with solvent naphtha, acetone, and isopropyl alcohol (all at room temperature) for 10 minutes each. Also, 300 cc of isopropyl alcohol is put in the beaker D in advance and boiled on a hot plate.

  After ultrasonic cleaning of isopropyl alcohol at room temperature, a hanger was immersed in a beaker D containing boiled isopropyl alcohol and heated for 5 minutes. After heating, the hanger was quickly pulled up and the substrate was taken out with tweezers so that the boiled foam did not contact the substrate surface. The substrate surface was already dry when it was lifted.

  The substrate 1 cleaned in this manner was placed on the reaction tube of the MOCVD apparatus simultaneously with the substrate of Example 1, grown as described in Example 1, and the obtained nitride semiconductor was used as Sample 2.

  About the sample 1 of Example 1, and the sample 2 of the comparative example 1, PL intensity was compared using the photo-luminescence (PL) measuring apparatus. The excitation light used for the PL measurement 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 was about 20 times higher than the PL intensity of sample 2. This clearly shows the difference between whether or not isopropyl alcohol is boiled or not in organic cleaning of the substrate. By not boiling isopropyl alcohol, the adhesion of hydrocarbons to the substrate surface can be suppressed. The emission characteristics of a gallium nitride compound semiconductor having an InGaN well layer grown on the substrate could be improved.

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

(Example 2)
As in Example 1, a MOCVD apparatus was used as a cleaning substrate 6 in which 1 μm of GaN was stacked on a sapphire substrate.

  In addition, a total of seven 500 cc beakers A to G used in this cleaning are used. Beakers A to D were prepared the same as in Comparative Example 1.

First, after performing the same substrate cleaning and substrate drying as in Comparative Example 1, beaker E containing 300 cc of an aqueous solution of ammonia hydrogen peroxide at normal temperature (NH ₃ : H ₂ O ₂ : H ₂ O = 1: 1: 5) The hanger was dipped in, 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. with a hot plate), stirred for 5 minutes, and then ultrasonicated in a pure water overflow using the beaker G filled with pure water. Washing was performed. The substrate surface was dried with nitrogen blow.

  The same nitride semiconductor was produced from the substrate thus cleaned by the same growth method as in Example 1 and used as Sample 3.

  When the PL intensity of sample 3 was measured, it was 60% of the PL intensity of sample 1, which was significantly improved compared to the PL intensity of sample 2 in comparative example 1 being 5% of that of sample 1. It was.

  As a result, most of the hydrocarbons firmly adhered to the substrate surface by boiling the organic solvent (in this example, isopropyl alcohol) in substrate cleaning or substrate drying can be removed by performing alkali cleaning and acid cleaning. did it.

(Example 3)
As in Example 1, a MOCVD apparatus was used as a cleaning substrate 1 having a sapphire substrate laminated with 1 μm of GaN.

  In this example, after performing the same substrate cleaning and substrate drying as in Comparative Example 1, 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 thus cleaned by the same growth method as in Example 1 and used as Sample 4.

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

  From this, it is possible to remove many of the hydrocarbons firmly adhered to the substrate surface by boiling the organic solvent (in this example, isopropyl alcohol) in substrate cleaning or substrate drying by performing ultraviolet ozone cleaning. did it.

Example 4
In the same manner as in Example 1, a MOCVD apparatus was used as a cleaning substrate in which 1 μm of GaN was stacked on a sapphire substrate.

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

  The same nitride semiconductor was produced from the substrate thus cleaned by the same growth method as in Example 1 and used as Sample 5.

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

  From this, by not performing organic cleaning, it prevents the organic solvent itself from adhering to the substrate surface, and further, by performing alkaline cleaning and acid cleaning, contaminants such as organic matter attached before cleaning Most of it could be removed.

  In addition, in the case where a large amount of organic substances are attached to the substrate surface before cleaning, it is desirable to perform organic cleaning before performing alkali cleaning and acid cleaning as in Example 2 in order to enhance the cleaning effect. .

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

  FIG. 3 is a cross-sectional view showing a layer structure of a light emitting device made of a gallium nitride compound semiconductor to which a substrate cleaning method according to Example 2 of the present invention is applied.

  After stacking 120 μm-thick GaN on a sapphire substrate by HVPE (hydride vapor phase epitaxy), polishing is performed to a depth of 10 μm using diamond slurry (abrasive grains) to remove irregularities on the substrate surface. It was. After polishing, organic substances such as lubricating oil and wax during polishing and impurities were removed by organic cleaning, and then a damaged layer generated by machining on the GaN surface was removed by a reactive ion etching method. In this way, a substrate 6 having a surface made of GaN was formed.

  Seven (A to G) 500 cc beakers (made by Pyrex (registered trademark)) thoroughly placed in a hanger and sufficiently washed with hydrofluoric acid are prepared, and solvent naphtha, acetone, and isopropyl are prepared in the A to C beakers. 300 cc of alcohol was added. However, all the organic solvents in the three beakers are used at room temperature.

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

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

  Thereafter, the substrate 6 was placed on the filter paper with tweezers, and nitrogen was blown from the center of the substrate using a nitrogen gun to blow off moisture on the surface of the substrate to the periphery of the substrate, followed by drying and removal.

  Next, the hanger is put into a beaker D containing 300 cc of an alkaline aqueous solution in which ammonia, hydrogen peroxide, and water are mixed at a ratio of 1: 1: 5, stirred for 5 minutes, and then put into a beaker E containing pure water. After performing ultrasonic cleaning for 10 minutes while overflowing pure water, the substrate 6 was placed on the filter paper with tweezers, and nitrogen was blown from the center of the substrate 6 using a nitrogen gun to remove moisture on the substrate surface. It was blown off around the substrate and dried.

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

  The substrate 6 thus cleaned was placed on the substrate holder in the reaction tube of the MOCVD apparatus.

  First, while flowing nitrogen at 4 liters / minute, hydrogen at 4 liters / minute, and ammonia at 2 liters / minute, the temperature of the substrate 6 was raised from room temperature to 1050 ° C., and then held for 2 minutes. Dirt and moisture such as organic matter remaining on the surface of 6 were removed.

Thereafter, while maintaining the temperature of the substrate 6 at 1050 ° C., nitrogen and hydrogen are flown at 13 liters / minute and 3 liters / minute as carrier gases, respectively, ammonia is 4 liters / minute, TMG is 80 μmol / minute, 10 ppm dilution. SiH ₄ was supplied at a rate of 10 cc / min, and a first n-type cladding layer 7 made of Si-doped GaN was grown to a thickness of 2 μm.

After growing the first n-type cladding layer 7, the temperature of the substrate 6 is kept at 1050 ° C., and nitrogen and hydrogen are allowed to flow as carrier gases at 15 liters / minute and 3 liters / minute, respectively, and ammonia is supplied at 2 liters / minute, 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 TMG at 40 μmol / min and TMA at 3 μmol / min.

After the second n-type cladding layer 8 is grown, the supply of TMG and SiH ₄ is stopped, the substrate temperature is lowered to 700 ° C., and at 700 ° C., while supplying nitrogen as a carrier gas at 14 liters / minute, ammonia is supplied. A 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 by supplying 6 liters / minute, TMG at 4 μmol / minute, and TMI at 1 μmol / minute. .

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

After the formation of the intermediate layer 10, the temperature of the substrate 6 is maintained at 1050 ° C., and nitrogen and hydrogen are allowed to flow as carrier gases at 15 liters / minute and 3 liters / minute respectively, while ammonia is supplied at 2 liters / minute and TMG is added. The p-type cladding layer 11 made of Al _0.05 Ga _0.95 N doped with Mg was supplied at a thickness of 0.2 μm by supplying 40 μmol / min, TMA 3 μmol / min, and Cp ₂ Mg 0.4 μmol / min. Grown up.

After growing the p-type cladding layer 11, the supply of TMG, TMA and Cp ₂ Mg is stopped, and the temperature of the substrate 6 is cooled to about room temperature while flowing nitrogen at 18 liters / minute and ammonia at 2 liters / minute. Then, the wafer in which the gallium nitride compound semiconductor was laminated on the substrate 6 was taken out from the reaction tube.

The organometallic compounds TMG, TMI, TMA, and Cp ₂ Mg were all vaporized with a hydrogen carrier gas and supplied to the reaction tube.

  The laminated structure formed of the gallium nitride compound semiconductors formed in this manner has a thickness of 5 nm each for nickel (Ni) and gold (Au) on the surface thereof by vapor deposition without annealing. Then, the transparent 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 by CVD on the light transmissive electrode 12 and the exposed p-type clad layer 11 to react with the photolithography method. A mask made of an insulating film was formed by ion etching so as to cover the transparent electrode 12 and to expose a part of the surface of the p-type cladding layer 11.

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

After the above steps, the insulating film is once removed by wet etching, and a part of the surface of the light transmissive electrode 12 and the exposed first n-type cladding layer are formed by vapor deposition and photolithography. 7 is laminated with 0.1 μm-thick titanium (Ti) and 0.5 μm-thick Au to form an n-side electrode 13 and a p-side electrode 14, respectively. Thereafter, an insulating film (not shown) made of SiO _{2 having a} thickness of 0.2 μm covering the surface of the light transmissive electrode 12 was formed by plasma CVD and photolithography.

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

  After the chip is 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 are respectively connected to the electrodes on the stem with wires, and then resin molded to produce a light emitting device. Sample 3 was obtained. When this light emitting device was driven with a forward current of 20 mA, it emitted blue light 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 embodiment described above, 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, and can also be applied to a light emitting element such as a semiconductor laser using a gallium nitride compound semiconductor. It is.

  Since the hydrocarbon adhering to the substrate surface can be removed, it is useful as a cleaning method for a gallium nitride compound semiconductor growth substrate used in a light emitting device such as a light emitting diode or a semiconductor laser.

(A) The flowchart of the substrate cleaning process according to the first embodiment of the present invention, (B) The flowchart of the substrate cleaning process according to the second embodiment of the present invention, (C) The substrate cleaning according to the third embodiment of the present invention. Process flowchart, (D) flowchart of substrate cleaning process according to the fourth embodiment of the present invention. Sectional drawing showing the layer structure of the gallium nitride type compound semiconductor to which the cleaning method of the board | substrate which concerns on Examples 1-4 and Comparative Example 1 of this invention is applied Sectional drawing showing the layer structure of the light emitting element which consists of a gallium nitride type compound semiconductor to which the cleaning method of the substrate concerning Example 2 of the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 6 Substrate 2, 4 GaN layer 3 Well layer 5 Top layer 7 1st n-type cladding layer 8 2nd n-type cladding layer 9 Light emitting layer 10 Intermediate layer 11 P-type cladding layer 12 Light transmitting electrode 13 n side Electrode 14 p-side electrode

Claims (1)

A method for cleaning a gallium nitride compound semiconductor growth substrate before growing a gallium nitride compound semiconductor , wherein the substrate is cleaned with an organic solvent, and after the organic cleaning step, cleaning with an alkali is performed. After that, the process of removing the alkali attached to the substrate surface by ultrasonic cleaning in pure water overflow and drying and removing the moisture on the substrate surface by nitrogen blowing, and cleaning with acid, followed by pure water overflow A method for cleaning a substrate for growing a gallium nitride-based compound semiconductor , comprising: a step of substituting and removing acid adhering to the substrate surface by ultrasonic cleaning in the substrate and drying and removing moisture on the substrate surface by nitrogen blowing .

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