JP4028967B2 - Method for forming semiconductor layer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a III-V group compound semiconductor layer used in a light-emitting element that emits light in a short wavelength range from blue-violet light to ultraviolet light.
[0002]
[Prior art]
In recent years, as a light source for next-generation high-density optical discs, there has been a growing demand for light-emitting elements that emit light in a short wavelength range from blue-violet to ultraviolet light, and in particular, III containing gallium nitride (GaN) as a main component. -V Group compound semiconductor layers are actively researched and developed.
[0003]
By the way, in the III-V compound semiconductor layer mainly composed of gallium nitride grown by the metal organic chemical vapor deposition (MOVPE) method, a p-type impurity is introduced to reduce the resistance, but hydrogen passivation is performed. As a result, the hydrogen atoms are bonded to the p-type impurity, thereby inactivating the p-type impurity. For this reason, it is difficult to reduce the resistance of the p-type III-V compound semiconductor layer.
[0004]
Therefore, in JP-A-5-183189, after growing a p-type gallium nitride semiconductor layer on a substrate, the gallium nitride semiconductor layer is 500 ° C. or higher in an atmosphere substantially free of hydrogen. A technique for reducing the resistance of the p-type gallium nitride semiconductor layer by exhausting hydrogen from the p-type gallium nitride semiconductor layer and activating the p-type impurity by performing a heat treatment at a temperature of 1 mm is proposed. ing.
[0005]
Japanese Patent Laid-Open No. 5-183189 discloses that when the above-described heat treatment is performed on a p-type gallium nitride semiconductor layer, the resistivity of the p-type gallium nitride semiconductor layer is 1 × 10. ⁶ It is described that it can be reduced to about Ω · cm to several Ω · cm.
[0006]
[Problems to be solved by the invention]
However, the inventors of the present invention can reduce the resistivity of the p-type gallium nitride semiconductor layer even if the p-type gallium nitride semiconductor layer is subjected to a heat treatment at a temperature of 500 ° C. or higher in an atmosphere substantially free of hydrogen. 1 × 10 ⁶ We faced the fact that it cannot be reliably reduced to Ω · cm to several Ω · cm.
[0007]
In view of the above, an object of the present invention is to reliably reduce the resistance value of a p-type III-V compound semiconductor layer.
[0008]
[Means for Solving the Problems]
As a result of various studies on the measures that can achieve the above-mentioned object, the present inventors have caused a temperature gradient in the compound semiconductor layer or relaxed the stress of the compound semiconductor layer in the heating process of the heat treatment step. The compound semiconductor layer can eliminate the atoms that inactivate the p-type impurity, and the compound semiconductor has an atom that deactivates the p-type impurity when the compound semiconductor layer is rapidly cooled in the cooling process after heating. It was found that penetration into the layer can be suppressed. The present invention has been made on the basis of the above knowledge, and is specifically realized by a method of forming first to third semiconductor layers.
[0009]
The first method for forming a semiconductor layer according to the present invention includes a step of forming a III-V group compound semiconductor layer into which a p-type impurity has been introduced on a substrate, and a step of performing a heat treatment on the compound semiconductor layer. The heat treatment step includes a step of removing atoms inactivating the p-type impurity from the compound semiconductor layer by generating a temperature gradient in the compound semiconductor layer in the process of heating the compound semiconductor layer.
[0010]
According to the method for forming the first semiconductor layer, when the compound semiconductor layer is heated, a temperature gradient is generated in the compound semiconductor layer, whereby atoms that inactivate the p-type impurity can be eliminated from the compound semiconductor layer. Therefore, the resistance value of the compound semiconductor layer can be reliably reduced.
[0011]
In the first method for forming a semiconductor layer, the temperature gradient is preferably formed in a direction perpendicular to the substrate.
[0012]
In this way, atoms that inactivate the p-type impurity can be discharged from the entire surface of the compound semiconductor layer, so that the resistance value of the compound semiconductor layer can be reliably reduced.
[0013]
In the first method for forming a semiconductor layer, the process of heating the compound semiconductor layer is performed by heating the compound semiconductor layer at a temperature rising rate higher than 0.3 ° C./s, thereby causing the compound semiconductor layer to be perpendicular to the substrate. It is preferable to include a step of generating a temperature gradient of
[0014]
This ensures that a temperature gradient is generated inside the compound semiconductor layer so that the substrate side is high and the surface side is low, so that atoms that inactivate the p-type impurities are exposed from the surface of the compound semiconductor layer to the outside. Can be discharged reliably.
[0015]
In the first method for forming a semiconductor layer, the process of heating the compound semiconductor layer is performed by heating the compound semiconductor layer at a temperature rising rate higher than 10 ° C./s, whereby the temperature in the direction perpendicular to the substrate of the compound semiconductor layer is increased. It preferably includes a step of creating a gradient.
[0016]
In this way, an abrupt temperature gradient in which the substrate side is high and the surface side is low is surely generated inside the compound semiconductor layer, and atoms that inactivate the p-type impurity are externally exposed from the surface of the compound semiconductor layer. Can be discharged more reliably.
[0017]
In the first method for forming a semiconductor layer, the process of heating the compound semiconductor layer is performed by supplying a cooling gas in a pulsed manner to the surface of the compound semiconductor layer, thereby generating a temperature gradient in the direction perpendicular to the substrate in the compound semiconductor layer. It is preferable to include the process to make.
[0018]
This ensures that a temperature gradient is generated inside the compound semiconductor layer so that the substrate side is high and the surface side is low, so that atoms that inactivate the p-type impurities are exposed from the surface of the compound semiconductor layer to the outside. Can be discharged reliably.
[0019]
In this case, the process of heating the compound semiconductor layer is preferably performed in a nitrogen gas atmosphere, and the cooling gas is preferably hydrogen gas.
[0020]
In this way, in a normal heat treatment process, hydrogen gas having a higher thermal conductivity than nitrogen gas is used to create a temperature gradient inside the compound semiconductor layer such that the substrate side is high and the surface side is low. It can surely occur.
[0021]
In the first method for forming a semiconductor layer, the temperature gradient is preferably formed in a direction parallel to the substrate.
[0022]
In this way, the atoms that inactivate the p-type impurity can be discharged to the outside from the surface of the portion of the compound semiconductor layer where the temperature is low, so that the resistance value of the compound semiconductor layer can be reliably reduced.
[0023]
In the first method for forming a semiconductor layer, in the process of heating the compound semiconductor layer, the substrate is heated on the first tray set to the first temperature, and then the substrate is moved to the first tray and the first tray. It is preferable to include a step of generating a temperature gradient in a direction parallel to the substrate in the compound semiconductor layer by placing the second tray so as to straddle the second tray set to a second temperature lower than the temperature.
[0024]
In this way, a temperature gradient in a direction parallel to the substrate can be reliably generated inside the compound semiconductor layer.
[0025]
In the first method for forming a semiconductor layer, in the process of heating the compound semiconductor layer, the substrate is heated on the first tray set to the first temperature, and then the substrate is moved to the first tray and the first tray. The compound semiconductor layer is placed so as to straddle the second tray set to the second temperature lower than the temperature and the third tray set to the third temperature lower than the second temperature. Preferably, the method includes a step of generating a temperature gradient in a direction parallel to the substrate.
[0026]
In this way, a temperature gradient in a direction parallel to the substrate can be more reliably generated inside the compound semiconductor layer.
[0027]
In the first semiconductor layer formation method, the step of performing the heat treatment preferably includes a step of heating and cooling the compound semiconductor layer a plurality of times to generate a plurality of temperature gradients in the compound semiconductor layer. .
[0028]
This improves the efficiency of discharging the atoms that deactivate the p-type impurity from the compound semiconductor layer to the outside, so that the resistance value of the compound semiconductor layer can be more reliably reduced.
[0029]
In the first method for forming a semiconductor layer, the compound semiconductor layer preferably contains nitrogen as a group III element.
[0030]
In this way, it is possible to reduce the resistance value of the group III-V nitride semiconductor layer used in the light emitting element that emits light in a short wavelength region from blue-violet light to ultraviolet light.
[0031]
In this case, the compound semiconductor layer containing nitrogen is preferably a cladding layer, a contact layer, or a light guide layer of the light emitting element.
[0032]
In this manner, the operating voltage of the light emitting element can be reduced to reduce power consumption, thereby suppressing heat generation of the light emitting element and improving reliability.
[0033]
The second method for forming a semiconductor layer according to the present invention includes a step of forming a group III-V compound semiconductor layer into which a p-type impurity is introduced on a substrate, and a step of performing a heat treatment on the compound semiconductor layer. In the process of preparing and heat-treating, the compound semiconductor layer is rapidly cooled in the process of cooling after the compound semiconductor layer is heated, thereby preventing the atoms that inactivate the p-type impurity from entering the compound semiconductor layer. The process of carrying out is included.
[0034]
According to the second method for forming a semiconductor device, it is possible to suppress a situation in which atoms that inactivate p-type impurities enter the compound semiconductor layer in the cooling process after heating in the heat treatment step. Can be reduced.
[0035]
In the second method for forming a semiconductor layer, the step of cooling the compound semiconductor layer preferably includes a step of cooling the compound semiconductor layer at a temperature lowering rate higher than 0.3 ° C./s.
[0036]
In this way, it is possible to reliably suppress a situation in which atoms that inactivate the p-type impurity enter the compound semiconductor layer in the cooling process of the heat treatment step, and thus it is possible to reliably reduce the resistance value of the compound semiconductor layer. .
[0037]
In the second method for forming a semiconductor layer, the step of cooling the compound semiconductor layer preferably includes a step of cooling the compound semiconductor layer at a temperature lowering rate higher than 10 ° C./s.
[0038]
In this way, it is possible to further reliably prevent the atoms that inactivate the p-type impurity from entering the compound semiconductor layer during the cooling process of the heat treatment step, and thus further reduce the resistance value of the compound semiconductor layer. Can do.
[0039]
In the second method for forming a semiconductor layer, the step of cooling the compound semiconductor layer preferably includes a step of supplying a cooling gas to the surface of the compound semiconductor layer.
[0040]
In this way, it is possible to reliably suppress a situation in which atoms that inactivate the p-type impurity enter the compound semiconductor layer in the cooling process of the heat treatment step, and thus it is possible to reliably reduce the resistance value of the compound semiconductor layer. .
[0041]
When a cooling gas is supplied to the surface of the compound semiconductor layer to rapidly cool the compound semiconductor layer, the process of cooling the compound semiconductor layer is performed in a nitrogen gas atmosphere, and the cooling gas is preferably hydrogen gas.
[0042]
In this way, in a normal heat treatment process, hydrogen gas having a higher thermal conductivity than nitrogen gas is used to ensure that atoms that inactivate p-type impurities enter the compound semiconductor layer. Can be suppressed.
[0043]
In this case, the partial pressure of hydrogen gas is preferably 33% or more.
[0044]
In this way, it is possible to more reliably suppress the situation where atoms that inactivate the p-type impurity enter the compound semiconductor layer.
[0045]
When rapidly cooling the compound semiconductor layer by supplying a cooling gas to the surface of the compound semiconductor layer, the process of cooling the compound semiconductor layer includes a step of supplying a cooling gas when the temperature of the substrate is 500 ° C. or lower. Is preferred.
[0046]
In this way, it is possible to more reliably suppress the situation where atoms that inactivate the p-type impurity enter the compound semiconductor layer.
[0047]
In the second method for forming a semiconductor layer, the compound semiconductor layer preferably contains nitrogen as a group III element.
[0048]
In this way, it is possible to reduce the resistance value of the group III-V nitride semiconductor layer used in the light emitting element that emits light in a short wavelength region from blue-violet light to ultraviolet light.
[0049]
In this case, the compound semiconductor layer containing nitrogen is preferably a cladding layer, a contact layer, or a light guide layer of the light emitting element.
[0050]
In this manner, the operating voltage of the light emitting element can be reduced to reduce power consumption, thereby suppressing heat generation of the light emitting element and improving reliability.
[0051]
The third method for forming a semiconductor layer according to the present invention includes a step of forming a group III-V compound semiconductor layer into which a p-type impurity has been introduced on a substrate, and a step of performing a heat treatment on the compound semiconductor layer. The step of preparing and performing the heat treatment includes a step of eliminating atoms inactivating the p-type impurity from the compound semiconductor layer by relaxing internal stress of the compound semiconductor layer in the process of heating the compound semiconductor layer. .
[0052]
According to the third method for forming a semiconductor layer, atoms that inactivate p-type impurities can be eliminated from the compound semiconductor layer by relaxing internal stress of the compound semiconductor layer when the compound semiconductor layer is heated. Therefore, the resistance value of the compound semiconductor layer can be reliably reduced.
[0053]
In the third method for forming a semiconductor layer, the step of heating the compound semiconductor layer preferably includes a step of relaxing internal stress of the compound semiconductor layer by changing the pressure of the atmosphere in which the substrate is placed.
[0054]
In this way, by changing the pressure in the annealing furnace in a normal heat treatment process, it is possible to easily and reliably suppress the situation where atoms that inactivate p-type impurities enter the compound semiconductor layer. it can.
[0055]
When the internal stress of the compound semiconductor layer is relieved by changing the pressure of the atmosphere in which the substrate is placed, the process of heating the compound semiconductor layer preferably includes a step of changing the pressure of the atmosphere higher than atmospheric pressure. .
[0056]
In this way, it is possible to more reliably suppress the situation where atoms that inactivate the p-type impurity enter the compound semiconductor layer.
[0057]
When relieving the internal stress of the compound semiconductor layer by changing the pressure of the atmosphere in which the substrate is placed, the process of heating the compound semiconductor layer is a step of changing the pressure of the atmosphere when the temperature of the substrate is 500 ° C. or lower. It is preferable to contain.
[0058]
In this way, it is possible to more reliably suppress the situation where atoms that inactivate the p-type impurity enter the compound semiconductor layer.
[0059]
In the third method for forming a semiconductor layer, the compound semiconductor layer preferably contains nitrogen as a group III element.
[0060]
In this way, it is possible to reduce the resistance value of the group III-V nitride semiconductor layer used in the light emitting element that emits light in a short wavelength region from blue-violet light to ultraviolet light.
[0061]
In this case, the compound semiconductor layer containing nitrogen is preferably a cladding layer, a contact layer, or a light guide layer of the light emitting element.
[0062]
In this manner, the operating voltage of the light emitting element can be reduced to reduce power consumption, thereby suppressing heat generation of the light emitting element and improving reliability.
[0063]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, a method for forming a semiconductor layer according to the first embodiment of the present invention will be described with reference to FIGS.
[0064]
In the first embodiment, a p-type compound semiconductor layer mainly composed of gallium nitride, for example, p-type Al, mainly used for a light emitting element (semiconductor laser element) having a short wavelength. _x Ga _1-x Although this is a method that can reduce the resistance of the N semiconductor layer (0 ≦ x ≦ 1), the first embodiment is similarly applied to other III-V compound semiconductor layers into which p-type impurities are introduced. can do.
[0065]
First, after cleaning the surface of the sapphire substrate 10 with an acidic solution, the sapphire substrate 10 is held in a susceptor in a reaction furnace (not shown) of the MOVPE apparatus, and then the inside of the reaction furnace is evacuated. To do. Next, after making the inside of the reaction furnace into a hydrogen atmosphere having a pressure of 40 kPa, the temperature of the reaction furnace is raised to about 1100 ° C. and the sapphire substrate 10 is heated, so that the surface of the sapphire substrate 10 is about 10%. Perform a minute of thermal cleaning.
[0066]
Next, after the temperature of the reactor is lowered to about 500 ° C., trimethylgallium (TMG) at a flow rate of 6 mL / min (standard state) and ammonia at a flow rate of 7.5 mL / min (standard state) are placed in the reactor. (NH _Three ) By simultaneously supplying a gas and hydrogen as a carrier gas, a low-temperature buffer layer 11 made of a GaN layer having a thickness of 20 nm is grown on the sapphire substrate 10.
[0067]
Next, the temperature of the reactor is raised to about 1000 ° C., and a GaN layer 12 having a thickness of 0.5 μm is grown on the low temperature buffer layer 11.
[0068]
Next, in the reactor, 1.7 mL / min (standard state) trimethylaluminum (TMA) and 30 mL / min (standard state) biscyclopentadienylmagnesium (Cp ₂ P-type Al having a thickness of 0.7 μm on the GaN layer 12. _0.07 Ga _0.93 N layer 13 is grown.
[0069]
Next, the sapphire substrate 10 is transferred from the reaction furnace of the MOVPE apparatus to the annealing furnace, and after placing the sapphire substrate 10 on the tray in the annealing furnace, the annealing furnace is once evacuated and then put into the annealing furnace. Nitrogen gas is introduced at a flow rate of 3 L / min (standard state) to bring the inside of the furnace to atmospheric pressure.
[0070]
Next, the tray on which the sapphire substrate 10 is placed is varied from 0.15 ° C. (0.15 ° C./s) to 150 ° C. (150 ° C./s) per second from room temperature (25 ° C.) to 750 ° C. P-type Al by heating at 750 ° C. for 1 hour and then cooling to room temperature at a rate of 10 ° C. (10 ° C./s) per second. _0.07 Ga _0.93 Heat treatment is performed on the N layer 13. In this heat treatment step, nitrogen gas is continuously introduced into the annealing furnace at a flow rate of 3 mL / min (standard state) to keep the furnace at atmospheric pressure.
[0071]
When the heat treatment process is completed, the sapphire substrate 10 is taken out of the annealing furnace and then p-type Al. _0.07 Ga _0.93 After forming a mask having openings of 2 mm in diameter at the four corners of a square having a side of 5 mm on the upper surface of the N layer 13, the sapphire substrate 10 is transferred to a vacuum deposition apparatus.
[0072]
Next, in a vacuum deposition apparatus, p-type Al is formed by resistance heating. _0.07 Ga _0.93 After a magnesium (Mg) film having a thickness of about 5 nm is deposited on the upper surface of the N layer 13 through a mask, a gold (Au) electrode having a thickness of about 200 nm is deposited on the magnesium film by an electron beam (EB). P-type Al _0.07 Ga _0.93 A circular electrode (test electrode) having a diameter of 2 mm is formed on the N layer 13. The magnesium film is p-type Al. _0.07 Ga _0.93 It is provided to facilitate the ohmic contact between the N layer 13 and the gold electrode.
[0073]
Next, after the sapphire substrate 10 is taken out from the vacuum deposition apparatus, the sapphire substrate 10 is cut into a 5 mm square chip shape so that the circular electrodes are positioned at the four corners, and then p-type Al _0.07 Ga _0.93 In order to evaluate the electrical characteristics of the N layer 13, hole measurement is performed at room temperature.
[0074]
FIG. 2 shows the temperature rise rate and p-type Al in the heat treatment process. _0.07 Ga _0.93 FIG. 2 shows the relationship with the resistivity of the N layer 13. As is apparent from FIG. 2, the resistivity is about 5 Ω · cm when the rate of temperature rise is 0.3 ° C./s or less. When the rate is higher than 0.3 ° C./s, the resistivity rapidly decreases. Further, when the rate of temperature rise is higher than 10 ° C./s, the resistivity becomes constant at about 4 Ω · cm. That is, when the temperature rising rate becomes higher than 10 ° C./s, the reduction in resistivity is saturated.
[0075]
The reason why the resistivity rapidly decreases when the temperature rising rate becomes higher than 0.3 ° C./s is considered as follows. That is, since the temperature rising rate is high, the sapphire substrate 10 and the p-type Al _0.07 Ga _0.93 A temperature difference occurs between the N layer 13 and the p-type Al. _0.07 Ga _0.93 A steep temperature gradient in the stacking direction (direction perpendicular to the substrate) is generated inside the N layer 13. The hydrogen atom that deactivates the p-type impurity (Mg) is p-type Al. _0.07 Ga _0.93 The hydrogen atom inactivating the p-type impurity (Mg) is transferred to the p-type Al in order to move from the high temperature portion (substrate side portion) in the N layer 13 to the low temperature portion (surface side portion). _0.07 Ga _0.93 In order to move from a high temperature part (substrate side part) in the N layer 13 to a low temperature part (surface side part), p-type Al _0.07 Ga _0.93 It is efficiently discharged from the surface of the N layer 13.
[0076]
Therefore, when the heating process of the heat treatment step is performed at a temperature rising rate higher than 0.3 ° C./s, hydrogen atoms inactivating the p-type impurities can be efficiently discharged, and more particularly than 10 ° C./s. When heated at a high temperature rise rate, the discharge efficiency of hydrogen atoms is further improved.
[0077]
In addition, the above-mentioned experiment is a p-type Al whose Al composition is 7%. _0.07 Ga _0.93 P-type Al whose Al composition is higher than 7%. _x Ga _1-x For the N layer (0.07 <x ≦ 1), when heated at a temperature rising rate higher than 10 ° C./s, hydrogen atoms inactivating the p-type impurities can be efficiently discharged. In particular, when heating at a heating rate of 150 ° C./s or more, the efficiency of discharging hydrogen atoms is further improved.
[0078]
(Modification of the first embodiment)
In the heat treatment step in the first embodiment, after the tray on which the sapphire substrate 10 is placed is heated from room temperature (25 ° C.) to 750 ° C. at a temperature rising rate of 10 ° C. (10 ° C./s), In the heating process at a temperature of 750 ° C., p-type Al _0.07 Ga _0.93 Hydrogen gas is introduced into the surface of the N layer 13 as a cooling gas in a pulsed manner (the hydrogen gas introduction process for 10 seconds and the hydrogen gas non-introduction process for 10 seconds are repeated), and then the temperature of the tray is set to room temperature. Experiments were also conducted to cool down. In this case, in the hydrogen gas non-introduction step, only nitrogen gas having a flow rate of 3 L / min (standard state) is introduced, and in the hydrogen gas introduction step, nitrogen gas having a flow rate of 2 L / min (standard state) and 1 L / min ( A mixed gas (hydrogen gas partial pressure: 33.3%) with hydrogen gas at a flow rate in a standard state is introduced.
[0079]
In this way, p-type Al _0.07 Ga _0.93 Since a steep temperature gradient in the stacking direction (direction perpendicular to the substrate) is generated inside the N layer 13, the hydrogen atoms that deactivate the p-type impurity (Mg) are p-type Al. _0.07 Ga _0.93 In order to move from a high temperature part (substrate side part) in the N layer 13 to a low temperature part (surface side part), p-type Al _0.07 Ga _0.93 It is efficiently discharged from the surface of the N layer 13.
[0080]
By the way, in 1st Embodiment and its modification, although the heat processing process was 1 time, it replaces with this and it is preferable to perform a heat processing process (a heating process and a cooling process) in multiple times. In this way, p-type Al _0.07 Ga _0.93 Since a rapid temperature gradient in the stacking direction is generated a plurality of times inside the N layer 13, the hydrogen atoms that deactivate the p-type impurity (Mg) are p-type Al _0.07 Ga _0.93 More efficiently discharged from the surface of the N layer 13.
[0081]
(Second Embodiment)
Hereinafter, a method for forming a semiconductor layer according to the second embodiment of the present invention will be described with reference to FIGS.
[0082]
The second embodiment is a p-type compound semiconductor layer mainly composed of gallium nitride, for example, p-type Al, which is mainly used for a light emitting device (semiconductor laser device) having a short wavelength. _x Ga _1-x Although this is a method capable of realizing a low resistance of the N semiconductor layer (0 ≦ x ≦ 1), the second embodiment is similarly applied to other III-V group compound semiconductor layers into which p-type impurities are introduced. can do.
[0083]
First, similarly to the first embodiment, a p-type Al having a thickness of 0.7 μm is formed on the sapphire substrate 10 via the low-temperature buffer layer 11 and the GaN layer 12 by the MOVPE method. _0.07 Ga _0.93 N layer 13 is grown.
[0084]
Next, the sapphire substrate 10 is transferred from the reaction furnace of the MOVPE apparatus to the annealing furnace, and after placing the sapphire substrate 10 on the tray in the annealing furnace, the annealing furnace is once evacuated and then put into the annealing furnace. Nitrogen gas is introduced at a flow rate of 3 L / min (standard state) to bring the inside of the furnace to atmospheric pressure.
[0085]
Next, the tray on which the sapphire substrate 10 is placed is heated from room temperature (25 ° C.) to 750 ° C. at a rate of temperature increase of 10 ° C. (10 ° C./s) per second, and then at a temperature of 750 ° C. for 1 hour. P-type Al by holding and then cooling to room temperature at various cooling rates from 0.15 ° C. (0.15 ° C./s) to 150 ° C. (150 ° C./s) per second _0.07 Ga _0.93 A heat treatment process (heating process and cooling process) is performed on the N layer 13. In this heat treatment step, nitrogen gas is continuously introduced into the annealing furnace at a flow rate of 3 mL / min (standard state) to keep the furnace at atmospheric pressure.
[0086]
When the heat treatment process is completed, the sapphire substrate 10 is taken out of the annealing furnace and then p-type Al. _0.07 Ga _0.93 After forming a mask having openings of 2 mm in diameter at the four corners of a square having a side of 5 mm on the upper surface of the N layer 13, the sapphire substrate 10 is transferred to a vacuum deposition apparatus.
[0087]
Next, in a vacuum deposition apparatus, p-type Al is formed by resistance heating. _0.07 Ga _0.93 After a magnesium (Mg) film having a thickness of about 5 nm is deposited on the upper surface of the N layer 13 through a mask, a gold (Au) electrode having a thickness of about 200 nm is deposited on the magnesium film by an electron beam (EB). P-type Al _0.07 Ga _0.93 A circular electrode (test electrode) having a diameter of 2 mm is formed on the N layer 13.
[0088]
Next, after the sapphire substrate 10 is taken out from the vacuum deposition apparatus, the sapphire substrate 10 is cut into a 5 mm square chip shape so that the circular electrodes are positioned at the four corners, and then p-type Al _0.07 Ga _0.93 In order to evaluate the electrical characteristics of the N layer 13, hole measurement was performed at room temperature.
[0089]
FIG. 3 shows the temperature drop rate and p-type Al in the cooling process after heating in the heat treatment process. _0.07 Ga _0.93 FIG. 3 shows the relationship with the resistivity of the N layer 13. As is clear from FIG. 3, the resistivity is about 5 Ω · cm when the temperature drop rate is 0.3 ° C./s or less. When the temperature is higher than 0.3 ° C./s, the resistivity rapidly decreases. Further, when the rate of temperature decrease is higher than 10 ° C./s, the resistivity becomes constant at about 4 Ω · cm. That is, when the rate of temperature decrease is higher than 10 ° C./s, the reduction in resistivity is saturated.
[0090]
The reason why the resistivity rapidly decreases when the temperature drop rate is higher than 0.3 ° C./s is considered as follows. That is, since the temperature drop rate is high, the sapphire substrate 10 and thus the p-type Al _0.07 Ga _0.93 Since the N layer 13 is rapidly cooled, hydrogen atoms that inactivate the p-type impurity (Mg) become p-type Al in the cooling process. _0.07 Ga _0.93 The situation of entering the N layer 13 is suppressed, and as a result, p-type Al _0.07 Ga _0.93 The resistivity of the N layer 13 can be greatly reduced.
[0091]
Therefore, if the cooling process after heating in the heat treatment step is performed at a temperature lowering rate higher than 0.3 ° C./s, it is possible to suppress the intrusion of hydrogen atoms that inactivate the p-type impurities, and more particularly than 10 ° C./s. When cooled at a high temperature-decreasing rate, intrusion of hydrogen atoms can be further suppressed.
[0092]
In addition, the above-mentioned experiment is a p-type Al whose Al composition is 7%. _0.07 Ga _0.93 P-type Al whose Al composition is higher than 7%. _x Ga _1-x When the N layer (0.07 <x ≦ 1) is cooled at a temperature lowering rate higher than 10 ° C./s, hydrogen atoms that inactivate p-type impurities can be efficiently discharged. The effect of suppressing the penetration of hydrogen atoms, which is cooled at a temperature drop rate of at least ° C./s, is further improved.
[0093]
(Third embodiment)
A method for forming a semiconductor layer according to the third embodiment of the present invention will be described below with reference to FIGS.
[0094]
The third embodiment is a p-type compound semiconductor layer mainly composed of gallium nitride, for example, p-type Al, which is mainly used for a light emitting device (semiconductor laser device) having a short wavelength. _x Ga _1-x Although this is a method that can reduce the resistance of the N semiconductor layer (0 ≦ x ≦ 1), the third embodiment is similarly applied to other III-V compound semiconductor layers into which p-type impurities are introduced. can do.
[0095]
First, similarly to the first embodiment, a p-type Al having a thickness of 0.7 μm is formed on the sapphire substrate 10 via the low-temperature buffer layer 11 and the GaN layer 12 by the MOVPE method. _0.07 Ga _0.93 N layer 13 is grown.
[0096]
Next, the sapphire substrate 10 is transferred from the reaction furnace of the MOVPE apparatus to the annealing furnace, and after placing the sapphire substrate 10 on the tray in the annealing furnace, the annealing furnace is once evacuated and then put into the annealing furnace. Nitrogen gas is introduced at a flow rate of 3 L / min (standard state) to bring the inside of the furnace to atmospheric pressure.
[0097]
Next, the tray on which the sapphire substrate 10 is placed is heated from room temperature (25 ° C.) to 750 ° C. at a rate of temperature increase of 10 ° C. (10 ° C./s) per second, and then at a temperature of 750 ° C. for 1 hour. Hold and then cool the tray temperature to room temperature, p-type Al _0.07 Ga _0.93 Heat treatment is performed on the N layer 13.
[0098]
As a feature of the third embodiment, in the cooling process after heating in the heat treatment step, a mixed gas of nitrogen gas and hydrogen gas, for example, nitrogen gas at a flow rate of 2 L / min (standard state) and 1 L / min in an annealing furnace. Mixed gas (hydrogen gas partial pressure: 33%) with a flow rate of min (standard state) hydrogen gas or nitrogen gas with a flow rate of 1 L / min (standard state) and hydrogen with a flow rate of 2 L / min (standard state) A gas mixture with gas (partial pressure of hydrogen gas: 67%) is continuously introduced to keep the inside of the furnace at atmospheric pressure.
[0099]
Thus, when hydrogen gas is introduced into the annealing furnace in the cooling process after heating, the thermal conductivity of the hydrogen gas is larger than that of the nitrogen gas. _0.07 Ga _0.93 Since the surface of the N layer 13 is rapidly cooled, hydrogen atoms that inactivate the p-type impurity (Mg) become p-type Al. _0.07 Ga _0.93 The situation of entering the N layer 13 is suppressed, and as a result, p-type Al _0.07 Ga _0.93 The resistivity of the N layer 13 can be greatly reduced.
[0100]
When the heat treatment process is completed, the sapphire substrate 10 is taken out of the annealing furnace and then p-type Al. _0.07 Ga _0.93 After forming a mask having openings of 2 mm in diameter at the four corners of a square having a side of 5 mm on the upper surface of the N layer 13, the sapphire substrate 10 is transferred to a vacuum deposition apparatus.
[0101]
Next, in a vacuum deposition apparatus, p-type Al is formed by resistance heating. _0.07 Ga _0.93 After a magnesium (Mg) film having a thickness of about 5 nm is deposited on the upper surface of the N layer 13 through a mask, a gold (Au) electrode having a thickness of about 200 nm is deposited on the magnesium film by an electron beam (EB). P-type Al _0.07 Ga _0.93 A circular electrode (test electrode) having a diameter of 2 mm is formed on the N layer 13.
[0102]
Next, after the sapphire substrate 10 is taken out from the vacuum deposition apparatus, the sapphire substrate 10 is cut into a 5 mm square chip shape so that the circular electrodes are positioned at the four corners, and then p-type Al _0.07 Ga _0.93 In order to evaluate the electrical characteristics of the N layer 13, hole measurement was performed at room temperature.
[0103]
FIG. 4 shows the partial pressure of hydrogen gas in the mixed gas introduced into the annealing furnace in the cooling process after heating and p-type Al. _0.07 Ga _0.93 The relationship with the resistivity of the N layer 13 is shown. As can be seen from FIG. 4, when the partial pressure of hydrogen gas increases, that is, when the amount of hydrogen gas introduced increases, the effect of rapid cooling is promoted and the resistivity decreases. It can also be seen that the resistivity, which is about 4 Ω · cm when the partial pressure of hydrogen gas is 0%, can be reduced to about 3.5 Ω · cm when the partial pressure of hydrogen gas is 33%. However, even when the partial pressure of hydrogen gas becomes 67% or more, the resistivity is constant at about 3.5 Ω · cm, and it is considered that the cooling effect by introducing hydrogen gas is saturated.
[0104]
By the way, in the cooling process after heating, only nitrogen gas at a flow rate of 3 L / min (standard state) is introduced from 750 ° C. to 500 ° C., and nitrogen at a flow rate of 2 L / min (standard state) from 500 ° C. to room temperature. An experiment was also conducted in which a mixed gas (hydrogen gas partial pressure: 33%) of a gas and hydrogen gas at a flow rate of 1 L / min (standard state) was introduced. That is, when the substrate temperature is 500 ° C. or lower, a cooling gas (hydrogen gas) is introduced to form p-type Al. _0.07 Ga _0.93 An experiment for rapidly cooling the N layer 13 was performed.
[0105]
In this case, p-type Al _0.07 Ga _0.93 It was found that the resistivity of the N layer 13 can be reduced to about 3 Ω · cm. This is because the p-type Al is reduced by setting the temperature when introducing hydrogen gas to 500 ° C. _0.07 Ga _0.93 This is considered to be because the situation where hydrogen atoms enter the N layer 13 can be further suppressed, and the inactivation of the p-type impurity can be further suppressed.
[0106]
(Fourth embodiment)
Hereinafter, a method for forming a semiconductor layer according to the fourth embodiment of the present invention will be described with reference to FIGS.
[0107]
The fourth embodiment is a p-type compound semiconductor layer mainly composed of gallium nitride, for example, p-type Al, which is mainly used for a light emitting element (semiconductor laser element) having a short wavelength. _x Ga _1-x Although this is a method capable of realizing a low resistance of the N semiconductor layer (0 ≦ x ≦ 1), the fourth embodiment is similarly applied to other III-V compound semiconductor layers into which p-type impurities are introduced. can do.
[0108]
First, similarly to the first embodiment, a p-type Al having a thickness of 0.7 μm is formed on the sapphire substrate 10 via the low-temperature buffer layer 11 and the GaN layer 12 by the MOVPE method. _0.07 Ga _0.93 N layer 13 is grown.
[0109]
Next, the sapphire substrate 10 is transferred from the reaction furnace of the MOVPE apparatus to the annealing furnace, and after placing the sapphire substrate 10 on the tray in the annealing furnace, the annealing furnace is once evacuated and then put into the annealing furnace. Nitrogen gas is introduced at a flow rate of 3 L / min (standard state) to bring the inside of the furnace to atmospheric pressure.
[0110]
Next, a first heat treatment process is performed on the sapphire substrate 10. That is, the tray on which the sapphire substrate 10 is placed is heated from room temperature (25 ° C.) to 750 ° C. at a temperature rising rate of 10 ° C./second (10 ° C./s) and then held at a temperature of 750 ° C. for 1 hour. Then, the temperature of the tray is cooled to room temperature. In the first heat treatment step, nitrogen gas is continuously introduced into the furnace at a flow rate of 3 mL / min (standard state) to keep the furnace at atmospheric pressure.
[0111]
Next, a second heat treatment process is performed on the sapphire substrate 10. That is, as in the first heat treatment step, the tray on which the sapphire substrate 10 is placed is heated from room temperature to 750 ° C. at a temperature rising rate of 10 ° C. (10 ° C./s), and then 750 ° C. Hold at temperature for 1 hour, then cool tray temperature to room temperature. In the second heat treatment step, nitrogen gas is continuously introduced into the furnace at a flow rate of 3 mL / min (standard state) to keep the inside of the furnace at atmospheric pressure.
[0112]
Thereafter, the same heat treatment process as the first and second heat treatment processes is performed, for example, four times. That is, for example, a total of six heat treatment steps are performed.
[0113]
When the six heat treatment steps are completed, the sapphire substrate 10 is taken out of the annealing furnace and then p-type Al. _0.07 Ga _0.93 After forming a mask having openings of 2 mm in diameter at the four corners of a square having a side of 5 mm on the upper surface of the N layer 13, the sapphire substrate 10 is transferred to a vacuum deposition apparatus.
[0114]
Next, in a vacuum deposition apparatus, p-type Al is formed by resistance heating. _0.07 Ga _0.93 A magnesium (Mg) film having a thickness of about 5 nm is deposited on the upper surface of the N layer 13 through a mask, and a gold (Au) electrode having a thickness of about 200 nm is deposited on the magnesium film by an electron beam (EB). P-type Al _0.07 Ga _0.93 A circular electrode (test electrode) having a diameter of 2 mm is formed on the N layer 13.
[0115]
Next, after the sapphire substrate 10 is taken out from the vacuum deposition apparatus, the sapphire substrate 10 is cut into a 5 mm square chip shape so that the circular electrodes are positioned at the four corners, and then p-type Al _0.07 Ga _0.93 In order to evaluate the electrical characteristics of the N layer 13, hole measurement was performed at room temperature.
[0116]
FIG. 5 shows the number of heat treatment steps and p-type Al. _0.07 Ga _0.93 The relationship with the resistivity of the N layer 13 is shown. FIG. 5 shows that the resistivity decreases from about 4.0 Ω · cm to about 3.5 Ω · cm as the number of heat treatment steps increases, and that the resistivity decreases when the number of heat treatment steps is four or more. It turns out to be saturated.
[0117]
By the way, an experiment was conducted in which the holding time at a temperature of 750 ° C. in each heat treatment step was changed from 1 hour to 6 hours. However, even if the holding time was increased, the resistance was the same as when the holding time was 1 hour. The rate was the same.
[0118]
Therefore, the heat treatment step with rapid heating having a temperature rising rate higher than 0.3 ° C./s is performed a plurality of times to obtain p-type Al. _0.07 Ga _0.93 By generating a plurality of temperature gradients inside the N layer 13, hydrogen gas discharge is promoted and p-type Al _0.07 Ga _0.93 The resistivity of the N layer 13 can be further reduced.
[0119]
(Fifth embodiment)
Hereinafter, a method of forming a semiconductor layer according to the fifth embodiment of the present invention will be described with reference to FIGS.
[0120]
The fifth embodiment is a p-type compound semiconductor layer mainly composed of gallium nitride, for example, p-type Al, which is mainly used for a light emitting device (semiconductor laser device) having a short wavelength. _x Ga _1-x Although this is a method capable of realizing a low resistance of the N semiconductor layer (0 ≦ x ≦ 1), the fifth embodiment is similarly applied to other III-V group compound semiconductor layers into which p-type impurities are introduced. can do.
[0121]
First, similarly to the first embodiment, a p-type Al having a thickness of 0.7 μm is formed on the sapphire substrate 10 via the low-temperature buffer layer 11 and the GaN layer 12 by the MOVPE method. _0.07 Ga _0.93 N layer 13 is grown.
[0122]
Next, the sapphire substrate 10 is transferred from the reaction furnace of the MOVPE apparatus to the annealing furnace, and after placing the sapphire substrate 10 on the tray in the annealing furnace, the annealing furnace is once evacuated and then put into the annealing furnace. Nitrogen gas is introduced at a flow rate of 3 L / min (standard state) to bring the inside of the furnace to atmospheric pressure.
[0123]
Next, the tray on which the sapphire substrate 10 is placed is heated from room temperature (25 ° C.) to 750 ° C. at a temperature rising rate of 10 ° C. (10 ° C./s) per second, and then at a temperature of 750 ° C. for 1 hour. And then lowered to room temperature at a rate of 10 ° C./second (10 ° C./s).
[0124]
As a feature of the fifth embodiment, in the heating process of the heat treatment process, nitrogen gas is continuously introduced into the annealing furnace at a flow rate of 3 mL / min (standard state), while discharging for discharging the gas in the annealing furnace. The pressure in the annealing furnace is controlled by adjusting a flow rate adjusting valve provided in the passage.
[0125]
In this way, p-type Al in the heating process _0.07 Ga _0.93 Since the compressive stress of the N layer 13 is relaxed, the hydrogen atoms that deactivate the p-type impurity (Mg) are converted into p-type Al. _0.07 Ga _0.93 It is discharged from the N layer 13 to the outside.
[0126]
When the heat treatment process is completed, the sapphire substrate 10 is taken out of the annealing furnace and then p-type Al. _0.07 Ga _0.93 After forming a mask having openings of 2 mm in diameter at the four corners of a square having a side of 5 mm on the upper surface of the N layer 13, the sapphire substrate 10 is transferred to a vacuum deposition apparatus.
[0127]
Next, in a vacuum deposition apparatus, p-type Al is formed by resistance heating. _0.07 Ga _0.93 After a magnesium (Mg) film having a thickness of about 5 nm is deposited on the upper surface of the N layer 13 through a mask, a gold (Au) electrode having a thickness of about 200 nm is deposited on the magnesium film by an electron beam (EB). P-type Al _0.07 Ga _0.93 A circular electrode (test electrode) having a diameter of 2 mm is formed on the N layer 13.
[0128]
Next, after the sapphire substrate 10 is taken out from the vacuum deposition apparatus, the sapphire substrate 10 is cut into a 5 mm square chip shape so that the circular electrodes are positioned at the four corners, and then p-type Al _0.07 Ga _0.93 In order to evaluate the electrical characteristics of the N layer 13, hole measurement was performed at room temperature.
[0129]
FIG. 6 shows the relationship between the atmospheric pressure during heat treatment at a temperature of 750 ° C. and the cross-sectional shape of the laminated film formed on the sapphire substrate 10, and when the atmospheric pressure becomes higher than atmospheric pressure, For example, when the pressure exceeds 1.5 atm, p-type Al _0.07 Ga _0.93 Since the compressive stress of the N layer 13 is greatly relieved, the hydrogen atoms that deactivate the p-type impurity (Mg) are converted into p-type Al. _0.07 Ga _0.93 Since it is efficiently discharged from the N layer 13 to the outside, p-type Al _0.07 Ga _0.93 The resistivity of the N layer 13 is reduced.
[0130]
By the way, in the process of heating the sapphire substrate 10 from room temperature to 750 ° C., the coefficient of thermal expansion of the sapphire substrate 10 is p-type Al. _0.07 Ga _0.93 Since the thermal expansion coefficient of the N layer 13 is smaller, as shown in FIG. 6, when the atmospheric pressure is 1.0 atm, p-type Al _0.07 Ga _0.93 Although compressive stress (indicated by an arrow) is generated in the N layer 13, the compressive stress is relaxed when the atmospheric pressure becomes 1.5 atm. This relaxation of the stress converts the hydrogen atoms that deactivate the p-type impurities into p-type Al. _0.07 Ga _0.93 Since it becomes a driving force to be discharged from the N layer 13 to the outside, p-type Al _0.07 Ga _0.93 The resistivity of the N layer 13 is reduced.
[0131]
In this case, if the atmospheric pressure remains 1.0 atm, p-type Al _0.07 Ga _0.93 The resistivity of the N layer 13 was about 4.0 Ω · cm, but it was confirmed that when the atmospheric pressure was 1.5, the resistivity was about 3.5 Ω · cm.
[0132]
In the process of heating the sapphire substrate 10, even if the atmospheric pressure is lower than atmospheric pressure, p-type Al _0.07 Ga _0.93 Although the compressive stress of the N layer 13 is relieved, when the atmospheric pressure is higher than the atmospheric pressure, the stress relieving effect is promoted and the resistivity is greatly reduced.
[0133]
In this embodiment, the temperature of the heat treatment step is set to 750 ° C. However, when the atmospheric pressure in the heating process is set higher than the atmospheric pressure, it is generally considered to be difficult to reduce the resistance to 500 ° C. Even at the following heat treatment temperatures, p-type Al _0.07 Ga _0.93 It was confirmed that the effect of relaxing the compressive stress of the N layer 13 was obtained.
[0134]
In this embodiment, the thermal expansion coefficient of the sapphire substrate 10 is p-type Al. _0.07 Ga _0.93 Since it is smaller than the thermal expansion coefficient of the N layer 13, p-type Al _0.07 Ga _0.93 Although compressive stress is generated in the N layer 13, tensile stress is generated in the compound semiconductor layer when the thermal expansion force of the substrate is larger than the thermal expansion force of the compound semiconductor layer. Also in this case, when the atmospheric pressure is made higher or lower than the atmospheric pressure, the tensile stress generated in the compound semiconductor layer is relaxed.
[0135]
(Sixth embodiment)
Hereinafter, a method for forming a semiconductor layer according to the sixth embodiment of the present invention will be described with reference to FIGS.
[0136]
In the sixth embodiment, a p-type compound semiconductor layer containing gallium nitride as a main component, for example, p-type Al, mainly used for a light emitting device (semiconductor laser device) having a short wavelength. _x Ga _1-x Although this is a method that can reduce the resistance of the N semiconductor layer (0 ≦ x ≦ 1), the sixth embodiment is similarly applied to other group III-V compound semiconductor layers into which p-type impurities are introduced. can do.
[0137]
First, similarly to the first embodiment, a p-type Al having a thickness of 0.7 μm is formed on the sapphire substrate 10 via the low-temperature buffer layer 11 and the GaN layer 12 by the MOVPE method. _0.07 Ga _0.93 N layer 13 is grown.
[0138]
Next, the sapphire substrate 10 on which the laminated film is formed is transferred from the reaction furnace of the MOVPE apparatus to the annealing furnace, and nitrogen gas is introduced at a flow rate of 3 L / min (standard state) so that the atmospheric pressure is maintained. Sapphire substrate 10 and then p-type Al _0.07 Ga _0.93 The N layer 13 is heat-treated as follows.
[0139]
First, as shown in FIG. 7, a first tray 21 heated to, for example, 750 ° C. by a first heater 21a, and a second heater 22a are placed on a heat sink 20 positioned in the annealing furnace. The second tray 22 heated to, for example, 570 ° C. and the third tray 23 heated to, for example, 375 ° C. by the third heater 23a are disposed, and the substrate 24 (sapphire transferred to the annealing furnace) is disposed. On the substrate 10, the low-temperature buffer layer 11, the GaN layer 12, and the p-type Al _0.07 Ga _0.93 A stacked body in which the N layer 13 is sequentially stacked is referred to as a substrate 24. ) On the first tray 21, the temperature of the first tray 21 is increased from room temperature (25 ° C.) to 750 ° C. at a temperature increase rate of 10 ° C. (10 ° C./s) per second. 24 is heated at a temperature of 750 ° C. for 1 hour.
[0140]
Next, the substrate 24 is moved in parallel by the substrate transfer tool 25 so that the substrate 24 straddles the first tray 21 set at 750 ° C. and the second tray 22 set at 570 ° C. Put. In this way, p-type Al _0.07 Ga _0.93 A sudden temperature gradient is generated in the N layer 13 in a direction parallel to the substrate. For this reason, the hydrogen atom inactivating the p-type impurity (Mg) is p-type Al. _0.07 Ga _0.93 Since it moves from a high temperature part (first tray side part) in the N layer 13 to a low temperature part (second tray side part), p-type Al _0.07 Ga _0.93 Efficiently discharged from N layer 13, p-type Al _0.07 Ga _0.93 The resistance value of the N layer 13 is reduced.
[0141]
When the heat treatment process is completed, the sapphire substrate 10 is taken out of the annealing furnace and then p-type Al. _0.07 Ga _0.93 After forming a mask having openings of 2 mm in diameter at the four corners of a square having a side of 5 mm on the upper surface of the N layer 13, the sapphire substrate 10 is transferred to a vacuum deposition apparatus.
[0142]
Next, in a vacuum deposition apparatus, p-type Al is formed by resistance heating. _0.07 Ga _0.93 After a magnesium (Mg) film having a thickness of about 5 nm is deposited on the upper surface of the N layer 13 through a mask, a gold (Au) electrode having a thickness of about 200 nm is deposited on the magnesium film by an electron beam (EB). P-type Al _0.07 Ga _0.93 A circular electrode (test electrode) having a diameter of 2 mm is formed on the N layer 13.
[0143]
Next, after the sapphire substrate 10 is taken out from the vacuum deposition apparatus, the sapphire substrate 10 is cut into a 5 mm square chip shape so that the circular electrodes are positioned at the four corners, and then p-type Al _0.07 Ga _0.93 In order to evaluate the electrical characteristics of the N layer 13, hole measurement was performed at room temperature. As a result, p-type Al _0.07 Ga _0.93 The resistance value of the N layer 13 was about 3.5 Ω · cm.
[0144]
In the sixth embodiment, the substrate 20 is placed so as to straddle the first tray 21 and the second tray 22, and p-type Al. _0.07 Ga _0.93 A temperature gradient is generated in the N layer 13 in a direction parallel to the substrate. Instead, the substrate 20 is placed so as to straddle the first tray 21, the second tray 22, and the third tray 23. P-type Al _0.07 Ga _0.93 A temperature gradient may be generated in the N layer 13 in a direction parallel to the substrate. Thus, when the substrate 20 is placed so as to straddle three trays having different temperatures, p-type Al _0.07 Ga _0.93 Since the temperature gradient generated in the N layer 13 becomes more steep, p-type Al _0.07 Ga _0.93 The resistance value of the N layer 13 is further reduced.
[0145]
(Seventh embodiment)
Hereinafter, a method for forming a semiconductor layer according to the seventh embodiment of the present invention will be described with reference to FIGS.
[0146]
The seventh embodiment reduces the operating current of the light emitting element by reducing the resistance of the p-type compound semiconductor layer used for the cladding layer, contact layer, or light guide layer of the light emitting element (laser element), This is a method for improving the reliability of the light emitting element.
[0147]
First, as shown in FIG. 8, a sapphire substrate 30 having a diameter of, for example, 5 cm is held by a susceptor in a reaction furnace (not shown) of the MOVPE apparatus, and then the reaction furnace is evacuated. Next, after making the inside of the reaction furnace into a hydrogen atmosphere having a pressure of 40 kPa, the temperature of the reaction furnace is raised to about 1100 ° C. and the sapphire substrate 20 is heated, so Perform a minute of thermal cleaning.
[0148]
Next, after the temperature of the reactor is lowered to about 500 ° C., trimethylgallium (TMG) with a flow rate of 6 mL / min (standard state) and a flow rate of 7.5 L / min (standard state) are put into the reactor. Ammonia (NH _Three ) A gas and a hydrogen as a carrier gas are simultaneously supplied to grow a low-temperature buffer layer (not shown) made of a GaN layer having a thickness of 20 nm on the sapphire substrate 20.
[0149]
Next, after raising the temperature of the reactor to about 1000 ° C., silane (SiH containing n-type impurities) is contained in the reactor. _Four ) A gas is supplied so that the impurity concentration of silicon is about 1 × 10 6 on the low-temperature buffer layer. ¹⁸ cm ^-3 And an n-type contact layer 31 made of an n-type GaN layer having a thickness of about 4 μm is grown.
[0150]
Next, by additionally supplying trimethylaluminum (TMA) at a flow rate of 1.7 mL / min into the reaction furnace, the impurity concentration of silicon is 5 × 10 5 on the n-type contact layer 31. ¹⁷ cm ^-3 N-type Al having a thickness of about 0.7 μm _0.07 Ga _0.93 An n-type cladding layer 32 made of an N layer is grown.
[0151]
Next, only the supply of trimethylaluminum (TMA) is stopped, and the impurity concentration of silicon is about 1 × 10 6 on the n-type cladding layer 32. ¹⁸ cm ^-3 And a first light guide layer 33 made of an n-type GaN layer having a thickness of about 100 nm is grown.
[0152]
Next, after the temperature of the reactor is lowered to about 800 ° C., the carrier gas is changed from hydrogen gas to ammonia gas, and trimethylindium (TMI) and trimethylgallium (TMG) are alternately supplied into the reactor. As a result, an In layer having a thickness of about 3 nm is formed on the first light guide layer 33. _0.1 Ga _0.9 An active layer 34 having a multiple quantum well structure including a quantum well layer (3 layers) made of N layers and a barrier layer (2 layers) made of a GaN layer having a thickness of about 9 nm is formed.
[0153]
Next, after raising the temperature of the reactor again to about 1000 ° C., the carrier gas is changed from nitrogen gas to hydrogen gas, and trimethylgallium (TMG), ammonia (NH _Three ) Gas and trimethylaluminum (TMA), p-type impurity biscyclopentadienylmagnesium (Cp) ₂ By supplying Mg 2 gas, the concentration of impurities made of magnesium is 5 × 10 5 on the active layer 34. ¹⁷ cm ^-3 P-type Al having a thickness of about 20 nm _0.15 Ga _0.85 A cap layer 35 made of an N layer is grown.
[0154]
Next, on the cap layer 35, the impurity concentration of magnesium is 1 × 10. ¹⁸ cm ^-3 After the second light guide layer 36 having a thickness of about 150 nm is grown, the impurity concentration of magnesium is 5 × 10 5 on the second light guide layer 36. ¹⁷ cm ^-3 P-type Al having a thickness of about 0.7 μm _0.07 Ga _0.93 A p-type cladding layer 37 made of an N layer is grown, and then the impurity concentration of magnesium is 1 × 10 1 on the p-type cladding layer 37. ¹⁸ cm ^-3 And a p-type contact layer 38 made of a p-type GaN layer having a thickness of about 0.1 μm is grown.
[0155]
Next, a heat treatment is performed on the III-V compound semiconductor layer into which the p-type impurity is introduced, for example, the second light guide layer 36, the p-type cladding layer 37, and the p-type contact layer 38. As a heat treatment method for these p-type III-V compound semiconductor layers, the semiconductor layer forming methods according to the first to sixth embodiments can be applied, but here, the fourth embodiment is applied. The case will be described.
[0156]
After the sapphire substrate 30 is transferred from the reaction furnace of the MOVPE apparatus to the annealing furnace and the sapphire substrate 30 is placed on the tray in the annealing furnace, the annealing furnace is once evacuated and then nitrogen gas is introduced into the annealing furnace. It is introduced at a flow rate of 3 L / min (standard state) to bring the inside of the furnace to atmospheric pressure.
[0157]
Next, the tray on which the sapphire substrate 30 is placed is heated from room temperature (25 ° C.) to 750 ° C. at a temperature rising rate of 10 ° C. (10 ° C./s) per second, and then at a temperature of 750 ° C. for 1 hour. Then, the first heat treatment is performed by cooling the temperature of the tray to room temperature. In the first heat treatment step, nitrogen gas is continuously introduced into the furnace at a flow rate of 3 mL / min (standard state) to keep the furnace at atmospheric pressure.
[0158]
Next, the tray on which the sapphire substrate 30 is placed is heated from room temperature (25 ° C.) to 750 ° C. at a temperature rising rate of 10 ° C. (10 ° C./s) per second, and then at a temperature of 750 ° C. for 1 hour. Then, a second heat treatment is performed by cooling the temperature of the tray to room temperature. In the second heat treatment step, nitrogen gas is continuously introduced into the furnace at a flow rate of 3 mL / min (standard state) to keep the inside of the furnace at atmospheric pressure.
[0159]
When the first and second heat treatment steps are completed, the n-type contact layer 31 is exposed by selective dry etching, and then a laminated film of a titanium film and an aluminum film on the upper surface of the n-type contact layer 31 An n-side electrode 39 made of is formed.
[0160]
Next, after the p-type contact layer 38 is processed into a ridge shape having a ridge width of about 2 μm, a striped p-side electrode made of a laminated film of a nickel film and a gold film is formed on the p-type contact layer 38. 40 is formed. In this case, the n-side electrode 39 and the p-side electrode 40 are made of silicon dioxide (SiO 2). ₂ ).
[0161]
Next, the laminate is cleaved to form a light emitting element (semiconductor laser element) having a resonator length of 750 μm, and then silicon dioxide and titanium dioxide (TiO 2) are formed on one of the cleavage surfaces of the resonator. ₂ ) And a highly reflective coating layer having a reflectance of 90% is formed to obtain a light emitting device (semiconductor laser device).
[0162]
According to the seventh embodiment, with respect to a group III-V compound semiconductor layer into which a p-type impurity is introduced, for example, the second light guide layer 36, the p-type cladding layer 37, or the p-type contact layer 38, 2 Since the heat treatment is performed once, the atoms inactivating the impurities of the second light guide layer 36, the p-type cladding layer 37, or the p-type contact layer 38 can be eliminated, and thereby, the compound semiconductor layers The resistance value can be reliably reduced.
[0163]
The laser element characteristics of the light emitting element obtained by performing twice the heat treatment for heating from room temperature to 750 ° C. at a temperature rising rate of 10 ° C./s were measured (corresponding to the fourth embodiment). Al _0.07 Ga _0.93 The resistivity of the p-type cladding layer 37 made of the N layer is about 3.5 Ω · cm, and is obtained by performing heat treatment once from room temperature to 750 ° C. at a rate of 0.3 ° C./s. (Equivalent to the first embodiment) When the laser element characteristics of the light emitting element were measured, p-type Al _0.07 Ga _0.93 The resistivity of the p-type cladding layer 37 made of the N layer was about 5 Ω · cm.
[0164]
FIG. 9 shows the relationship between the operating voltage of the light emitting element and the threshold current when the resistivity of the p-type cladding layer 37 is about 3.5 Ω · cm and about 5 Ω · cm. It can be seen that when the resistivity of the cladding layer 37 is low, the operating current is reduced when the threshold current is kept constant. For example, when the resistivity of the p-type cladding layer 37 is about 3.5 Ω · cm, the operating current when the threshold current is 50 mA is 5 V and the power consumption is about 0.25 W. When the resistivity of 37 is about 5 Ω · cm, the operating current when the threshold current is 60 mA is 6 V, and the power consumption is about 0.36 W.
[0165]
From these facts, when the method for forming a semiconductor layer according to the first to sixth embodiments is applied to a group III-V compound semiconductor layer into which a p-type impurity has been introduced, the operating voltage of the obtained light emitting element is reduced. Thus, power consumption can be reduced, whereby heat generation of the light-emitting element can be suppressed and reliability can be improved.
[0166]
In the first to sixth embodiments, the sapphire substrate is used as the substrate, but a silicon carbide substrate may be used instead.
[0167]
【The invention's effect】
According to the first method for forming a semiconductor layer according to the present invention, when the compound semiconductor layer is heated, a temperature gradient is generated in the compound semiconductor layer, thereby inactivating the p-type impurity from the compound semiconductor layer. Since atoms can be eliminated, the resistance value of the compound semiconductor layer can be reliably reduced.
[0168]
According to the second method for forming a semiconductor device of the present invention, it is possible to suppress a situation in which atoms that inactivate the p-type impurity enter the compound semiconductor layer in the cooling process of the heat treatment step. Can be reduced.
[0169]
According to the third method for forming a semiconductor layer according to the present invention, when the compound semiconductor layer is heated, the internal stress of the compound semiconductor layer is relaxed, thereby inactivating the p-type impurity from the compound semiconductor layer. Since atoms can be eliminated, the resistance value of the compound semiconductor layer can be reliably reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a laminated structure that is an object of a method for forming a semiconductor layer according to first to sixth embodiments.
FIG. 2 shows a temperature rise rate and p-type Al in the heat treatment step of the semiconductor layer forming method according to the first embodiment. _0.07 Ga _0.93 It is a characteristic view which shows the relationship with the resistivity of N layer.
FIG. 3 shows a temperature drop rate and p-type Al in the cooling process after heating in the heat treatment step of the semiconductor layer forming method according to the second embodiment. _0.07 Ga _0.93 It is a characteristic view which shows the relationship with the resistivity of N layer.
FIG. 4 shows partial pressure of hydrogen gas in a mixed gas introduced into an annealing furnace and p-type Al in a cooling process after heating in a heat treatment step of a semiconductor layer forming method according to a third embodiment. _0.07 Ga _0.93 It is a characteristic view which shows the relationship with the resistivity of N layer.
FIG. 5 shows the number of heat treatment steps and p-type Al in the method for forming a semiconductor layer according to the fourth embodiment. _0.07 Ga _0.93 It is a characteristic view which shows the relationship with the resistivity of N layer.
FIG. 6 is a cross-sectional view showing the relationship between the atmospheric pressure during heat treatment and the cross-sectional shape of a laminated film formed on a sapphire substrate in the semiconductor layer forming method according to the fifth embodiment.
FIG. 7 shows p-type Al in the method for forming a semiconductor layer according to the sixth embodiment. _0.07 Ga _0.93 It is sectional drawing which shows the method of producing the temperature gradient parallel to a board | substrate in N layer.
FIG. 8 is a cross-sectional view of a light emitting device that is an object of a method for forming a semiconductor layer according to a seventh embodiment.
FIG. 9 is a characteristic diagram showing a relationship between an operating voltage and a threshold current of a light emitting device obtained by the semiconductor layer forming method according to the seventh embodiment.
[Explanation of symbols]
10 Sapphire substrate
11 Low temperature buffer layer
12 GaN layer
13 p-type Al _0.07 Ga _0.93 N layers
20 Heat sink
21 First tray
21a First heater
22 Second tray
22a Second heater
23 Second tray
23a Third heater
24 Substrate
25 Substrate transport tool
30 Sapphire substrate
31 n-type contact layer
32 n-type cladding layer
33 First light guide layer
34 Active layer
35 Cap layer
36 Second light guide layer
37 p-type cladding layer
38 p-type contact layer
39 n-side electrode
40 p-side electrode

Claims (3)

forming a group III-V compound semiconductor layer into which a p-type impurity has been introduced on a substrate; and performing a heat treatment on the compound semiconductor layer,
The step of performing the heat treatment is performed by heating the compound semiconductor layer at a temperature rising rate higher than 10 ° C./s in the process of heating the compound semiconductor layer, thereby generating a temperature gradient in a direction perpendicular to the substrate. , look including the step of eliminating an atom from the compound semiconductor layer is made to inactivate the p-type impurity, the process of heating the compound semiconductor layer, the pulse supplying a cooling gas to the surface of the compound semiconductor layer forming a semiconductor layer-containing Mukoto wherein step of. It said step of heating the compound semiconductor layer is performed in a nitrogen gas atmosphere, forming a semiconductor layer according to claim 1, wherein the cooling gas is hydrogen gas.   The step of performing the heat treatment includes a step of heating and cooling the compound semiconductor layer a plurality of times to generate a temperature gradient in the compound semiconductor layer a plurality of times. Of forming a semiconductor layer.

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