JP5510467B2 - Manufacturing method of nitride semiconductor - Google Patents

Description

  The present invention relates to a method for manufacturing a nitride semiconductor for growing a nitride semiconductor layer on a sapphire substrate.

  Nitride semiconductors are researched, developed, and put to practical use as materials for light-emitting diodes (LEDs) that emit high-intensity ultraviolet light, blue light, green light, etc., and high-electron mobility transistors (HEMTs) for high-power applications. Has been done.

  A single crystal substrate of sapphire or silicon carbide, which is a heterogeneous substrate, is mainly used for crystal growth of nitride semiconductors. In particular, a sapphire substrate is widely used because it is stable at a general crystal growth temperature (around 1000 ° C.) of a nitride semiconductor, and a large-diameter substrate can be easily obtained at a low price.

  As a method for growing a nitride semiconductor on a sapphire substrate, a “two-stage growth method” using a metal organic vapor phase epitaxy (MOVPE method) is known (for example, see Patent Document 1).

  FIG. 5 shows a crystal growth method by a two-stage growth method, where (a) is a hydrogen cleaning step, (b) is a growth step of a low temperature growth buffer layer, (c) is a growth step of a single crystal nucleus, and (d) is a step of FIG. The growth process of a GaN layer is shown. FIG. 6 shows a temperature sequence in the two-stage growth method. In addition, (a)-(d) in FIG. 6 respond | corresponds to each process of FIG.

The two-stage growth method is performed by the following steps. (A) At a temperature of about 1200 ° C., hydrogen gas 102 is sprayed onto the surface of the sapphire substrate 101 to clean the substrate surface (hydrogen cleaning).
(B) A low temperature growth buffer layer 103 made of GaN, AlN or the like is grown on the sapphire substrate 101 in an atmosphere of 500 to 600 ° C. In this step, since the crystal growth temperature is lower than the melting point of GaN, AlN or the like, the polycrystalline low-temperature growth buffer layer 103 is formed.
(C) The sapphire substrate 101 and the low-temperature growth buffer layer 103 are heated (annealed) to about 1100 ° C. to partially form single crystal nuclei 104 in the low-temperature growth buffer layer 103.
(D) In a temperature atmosphere of about 1100 ° C., a GaN layer (epitaxial layer) 105 is grown on the low-temperature growth buffer layer 103 and the single crystal nucleus 104 using the single crystal nucleus 104 as a nucleus.

Incidentally, the conventional growth method before the two-step growth method has grown a nitride semiconductor directly on a sapphire substrate at a high temperature of 1000 ° C. or higher. However, it is difficult to obtain a nitride semiconductor film that continuously covers the entire surface of the sapphire substrate, and even when a continuous film is obtained, the dislocation density of the nitride semiconductor layer is very high, 10 ¹⁰ to 10 ¹¹ cm ^−. It was about ² . Since dislocations act as non-radiative recombination centers for electrons and holes, or as scattering centers, it is impossible to obtain practical device characteristics when applying nitride semiconductors manufactured by this method to semiconductor devices. there were.

The above-described two-stage growth method makes it possible to grow a nitride semiconductor layer applicable to devices on a sapphire substrate, and to reduce the dislocation density to about 10 ⁹ cm ^{-2 for} the first time. Various devices using nitride semiconductors can be put to practical use.

However, the above-described two-stage growth method has the following drawbacks.
(1) Compared with the conventional crystal growth of GaAs or InP-based semiconductors, the production efficiency is poor and is about half that of the conventional one. Conventional crystal growth not based on the two-step growth method is a simple temperature change from temperature rise to 500-600 ° C. (10 minutes) → growth (60 minutes) → temperature drop to room temperature (20 minutes) → removal. A small temperature sequence is common.

  On the other hand, as shown in FIG. 6, the growth of the nitride semiconductor by the two-step growth method is performed by raising the temperature from room temperature to 1200 ° C. (30 minutes) → hydrogen cleaning in the step (a) (10 minutes) → about 530 Decreasing temperature to 40 ° C. (40 minutes) → Growth of low temperature growth buffer layer 103 in step (b) (1 minute) → Temperature increase in step (c) (20 minutes) → GaN growth in step (d) (60 minutes) → The temperature sequence is complicated and has a large temperature change, such as temperature decrease (30 minutes) → room temperature (removal). For this reason, crystal growth time will be 3 hours or more, and production efficiency will worsen.

  For example, when a GaAs layer is grown on a GaAs substrate with a mass production apparatus, if the growth time is 1 hour, a total of 1.5 hours is required for 10 minutes for temperature increase, 1 hour for growth, and 20 minutes for temperature decrease. . On the other hand, when GaN is grown on the sapphire substrate, as shown in FIG. 6, (30 minutes + 10 minutes + 40 minutes + 1 minute + 20 minutes + 60 minutes + 30 minutes) = 191 minutes (3 hours 11 minutes). Compared with the conventional method of 90 minutes that does not depend on the growth method, the crystal growth time is significantly increased, and the production efficiency is reduced to half or less.

(2) The stability and reproducibility of crystal growth is poor. Regarding this problem, the present inventors conducted the following investigation on the reproducibility of the thickness of the GaN layer and the X-ray diffraction half width by the two-step growth method.

  FIG. 7 shows the thickness characteristics of the GaN layer when GaN growth is performed 100 times under the same conditions by the two-stage growth method, and FIG. 8 is a graph when GaN growth is performed 100 times under the same conditions by the two-stage growth method. The X-ray diffraction half-width characteristics of a GaN layer are shown. In addition, the temperature sequence followed FIG.

  In order to obtain the characteristics shown in FIGS. 7 and 8, GaN growth was performed according to the process shown in FIG. 5 under the following conditions. The low temperature growth buffer layer 103 shown in the step (b) is grown for 80 seconds by using trimethylgallium (TMG) as a raw material at 382 μmol / min, ammonia at 10 slm, carrier gas at 40 slm, and nitrogen at 100 slm, and has a thickness of about 25 nm. It was. The annealing process in the step (c) was performed by heating the sapphire substrate 101 to 1100 ° C. with 20 slm of ammonia, 30 slm of hydrogen, and 50 slm of nitrogen. Further, in the GaN layer 105 shown in the step (d), when the substrate temperature reached 1100 ° C., TMG was started to flow at a flow rate of 846 μmol / min, and GaN was grown for 30 minutes. After 30 minutes, the growth was completed with the TMG flow rate set to zero. Thereafter, the substrate temperature was lowered to room temperature, and the substrate was taken out. The average value of the thickness of the GaN layer 105 obtained in the step (d) was 1.5 μm, and the average value of the X-ray diffraction half width was 329 seconds.

  As a result, the characteristics shown in FIGS. 7 and 8 were obtained. As shown in FIGS. 7 and 8, both the thickness of the GaN layer and the X-ray diffraction half-value width by the two-step growth method greatly fluctuate with each growth (± 20% or more with respect to the average value). It turns out that property and stability are bad.

  Such instability of the two-step growth method is due to the formation of the single crystal nucleus 104 that becomes the growth starting point of the GaN layer 105 by the low-temperature buffer growth in the step (b) and the annealing in the step (c). doing. By annealing the low temperature growth buffer layer 103, single crystal nuclei 104 are formed, but there is also a process in which the low temperature growth buffer layer 103 gradually evaporates simultaneously with the progress of this process. The amount of evaporation of GaN in the vicinity of the growth temperature (up to 1000 ° C.) depends exponentially on the temperature, and even a slight temperature change causes a large amount of evaporation. For this reason, the amount and density of the single crystal nuclei 104 at the stage of starting growth vary, reflecting the slight difference in substrate temperature for each growth, and the above instability is caused.

  More specifically, at a high temperature of 1000 ° C. or higher, GaN hardly adheres directly to the surface of the sapphire substrate, and starts growing using the single crystal nucleus 104 as a growth base point. For this reason, the growth rate of the GaN layer 105 at the initial stage of growth depends on the density of the initial single crystal nuclei 104, and the fluctuation of the density of the single crystal nuclei 104 is the fluctuation of the final film thickness shown in FIG. Will appear as.

  Moreover, the fact that the X-ray diffraction half-value width varies greatly means that the dislocation density of the GaN layer 105 varies greatly. Dislocations occur inside single crystal nuclei that are the starting point of growth, or at boundaries where nuclei and nuclei fuse together by growth. Therefore, the higher the density of single crystal nuclei 104, the higher the dislocation density. For this reason, when the density of the single crystal nucleus 104 that is the starting point of growth varies, the dislocation density of the GaN layer 105 grown thereon also varies, and as a result, the X-ray diffraction half width varies as shown in FIG. .

  As a method for overcoming the drawbacks of such a two-step growth method, a sapphire substrate is heat-treated in a source gas containing nitrogen, a nitride region is formed on the surface of the sapphire substrate, and a GaN layer is grown on the nitride region. Is known (see, for example, Patent Documents 2 and 3). When the present inventor further tried this method, it was confirmed that the production efficiency was improved as compared with the two-stage growth method. That is, the growth sequence increases from room temperature to 1000 ° C. (30 minutes) → thermal nitridation in ammonia (30 minutes) → GaN growth (60 minutes) → temperature decrease to room temperature (30 minutes). Simplified. As a result, the total growth time was 2.5 hours, which was shorter than 3 hours 11 minutes in the two-stage growth method. Further, by this method, it was confirmed that the GaN layer can be grown because the nitrided region on the sapphire surface acts as a nucleus serving as the starting point of GaN growth.

  However, the thickness and the half width of the X-ray diffraction of the obtained GaN layer were poor in reproducibility, like GaN obtained by the two-step growth method. This is because the thickness of the nitrided region of the sapphire surface formed by thermal nitridation varies within a range of 5 to 35 nm for each experiment. The reason why the thickness of the nitrided region varies from experiment to experiment is not clear, but it is highly likely that the nitride on the sapphire surface formed by thermal nitridation is thermally unstable.

  Further, a method of nitriding the sapphire surface with plasma such as nitrogen gas instead of thermally nitriding the sapphire substrate surface is also known (see, for example, Patent Documents 4 and 5). As a result of additional tests, a flat film could be obtained by growing GaN on the nitrided surface by plasma CVD (raw materials were TMG and nitrogen).

  However, the half width of X-ray diffraction of the obtained GaN layer was about 1000 seconds, which was much larger than 329 seconds of the GaN layer formed by the two-step growth method. This means that the dislocation density is remarkably higher than that of the GaN layer formed by the two-step growth method, which causes a deterioration in reproducibility and stability.

  If nitrogen radicals are present on the surface during the growth of the GaN layer, the nitrogen radicals are very active, so they are immediately bonded to Ga atoms separated from TMG, and GaN is precipitated. As a result, the surface diffusion of Ga atoms on the growth surface is inhibited, and the growth rate in the lateral direction (parallel to the surface) of GaN is slowed. In this case, a continuous GaN layer that covers the entire sapphire surface can be obtained only when the density of nuclei, which is the starting point of growth formed on the surface of the sapphire substrate by plasma nitriding, is high, and as a result, continuous GaN When a layer is obtained, the dislocation density is increased.

On the other hand, in the MOVPE method used in the two-step growth method, there is no radical that inhibits the surface diffusion of Ga, so that the lateral growth rate of GaN is high, and even if the density of single crystal nuclei is low, continuous GaN A layer can be obtained, and therefore a film with a low dislocation density can be obtained.
Japanese Patent Publication No.8-8217 Japanese Patent Publication No. 7-54806 JP 2001-15443 A JP 11-87253 A JP 2001-217193 A

  However, according to the conventional nitride semiconductor manufacturing method, it is extremely difficult to form the thermal nitride on the surface of the sapphire substrate in a stable form. Further, when the surface of the sapphire substrate is nitrided by plasma and the plasma CVD method is used for GaN growth thereon, the characteristics of the obtained GaN crystal are significantly inferior to those of the conventional two-step growth method. For this reason, low production efficiency and instability of growth, which are disadvantages of the two-stage growth method, cannot be overcome while maintaining a film quality equivalent to or better than the GaN layer obtained by the two-stage growth method.

  Accordingly, an object of the present invention is to provide a nitride semiconductor manufacturing method capable of growing a GaN layer having a film quality equal to or higher than that of the two-step growth method on a sapphire substrate and obtaining high production efficiency and growth stability. Is to provide.

  In order to achieve the above object, the present invention provides a first step of forming a surface modified layer on a sapphire substrate and the sapphire substrate on which the surface modified layer is formed in an inert gas atmosphere or in a non-activated gas. A second step of raising the temperature to the growth temperature of the nitride semiconductor in an atmosphere in which hydrogen having a concentration of 10% or less is mixed in the active gas; and a third step of growing a nitride semiconductor layer on the surface of the surface modification layer A method of manufacturing a nitride semiconductor including the steps is provided.

  According to the method for producing a nitride semiconductor of the present invention, a GaN layer having a film quality equivalent to or higher than that of the two-step growth method can be grown on the sapphire substrate, and high production efficiency and growth stability can be obtained.

FIG. 1 shows a manufacturing process of a method for manufacturing a nitride semiconductor according to a first embodiment of the present invention, (a) shows a sapphire substrate, and (b) shows a manufacturing process of a surface modified layer. FIG. 4C is a diagram showing a manufacturing process of the GaN layer. FIG. 2 shows a temperature sequence in the growth method of FIG. 1, (a) is a temperature sequence diagram in the plasma nitriding step, and (b) is a temperature sequence diagram in the MOVPE growth step. FIG. 3 is a thickness characteristic diagram of a GaN layer when GaN growth is performed 100 times under the same conditions. FIG. 4 is an X-ray diffraction half-width characteristic diagram of a GaN layer when GaN growth is performed 100 times under the same conditions. 5A and 5B show a crystal growth method by a two-stage growth method, where FIG. 5A shows a hydrogen cleaning process, FIG. 5B shows a growth process of a low temperature growth buffer layer, and FIG. 5C shows growth of a single crystal nucleus. The figure which shows a process, (d) is a figure which shows the growth process of a GaN layer. FIG. 6 is a temperature sequence diagram in the two-stage growth method. FIG. 7 is a thickness characteristic diagram of the GaN layer when GaN growth is performed 100 times under the same conditions by the two-stage growth method. FIG. 8 shows the X-ray diffraction half-width characteristics of the GaN layer when GaN growth is performed 100 times by the two-stage growth method under the same conditions.

[First Embodiment]
(Nitride semiconductor manufacturing method)
1A and 1B show a manufacturing process of a nitride semiconductor manufacturing method according to a first embodiment of the present invention, FIG. 1A shows a sapphire substrate, and FIG. 1B shows a surface modification manufacturing process. (C) is a figure which shows the manufacturing process of a GaN layer. 2 shows a temperature sequence in the growth method of FIG. 1, (a) is a temperature sequence diagram in the plasma nitriding step, and (b) is a temperature sequence diagram in the MOVPE growth step.

First, a C-plane sapphire substrate (hereinafter simply referred to as a sapphire substrate) 1 is introduced into an electron cyclotron resonance (ECR) plasma apparatus (not shown), and the degree of vacuum in the ECR plasma apparatus is reduced to 1 × 10 ⁻⁹ Torr. After that, the temperature of the sapphire substrate 1 was raised from room temperature to 300 ° C. (FIG. 1A).

  Next, nitrogen gas was introduced into the ECR plasma apparatus at a predetermined flow rate (for example, 30 sccm) to obtain a predetermined degree of vacuum (for example, 7 mTorr). In this state, plasma was generated by irradiation with microwaves (for example, power of 100 W). By this plasma treatment, a surface modification layer (nitride layer) 2 having a predetermined thickness (for example, about 3 nm) was formed on the surface of the sapphire substrate 1 (FIG. 1B). In addition, the thickness of the surface modification layer 2 was calculated | required by the measurement of the X-ray reflectivity.

  The inventor has found that the thickness of the surface modified layer 2 obtained by nitriding the surface of the sapphire substrate 1 with plasma can be controlled with much higher reproducibility than in the case of thermal nitriding. This is because plasma nitridation is performed at a lower temperature than thermal nitridation, and thus the formed surface modification layer 2 is not lost by etching. Further, the density of the nitride forming the surface modification layer 2 can be estimated from the measurement of the X-ray reflectivity, but the nitride by plasma nitriding has a higher density than the case by thermal nitriding, It was also found that a dense nitride with high heat resistance was formed.

  Furthermore, the present inventor examined the temperature of the plasma treatment between room temperature and 600 ° C., and the microwave power between 100 and 500 W. As a result, it has been found that if the processing time is adjusted for each processing temperature and microwave power, and the thickness of the surface modification layer 2 is controlled to 1 to 10 nm, a result equivalent to the two-step growth method can be obtained. It was. When the thickness of the nitrided region was smaller than 1 nm, a part of the surface modification layer 2 was etched during the temperature increase, and the growth stability was impaired. Further, when the thickness of the surface modification layer 2 was larger than 10 nm, the dislocations of the GaN layer grown on the surface modification layer 2 increased significantly. This is because if the thickness of the surface modification layer 2 is large, the crystallinity on the surface side of the surface modification layer 2 is lowered.

  Next, as shown in FIG. 2 (a), the time required for plasma nitriding is as follows: temperature rise from room temperature to 300 ° C. (10 minutes) → plasma nitriding treatment (30 minutes) → temperature drop to room temperature (20 minutes), For a total of 1 hour.

Next, the sapphire substrate 1 subjected to nitriding treatment was introduced into an MOVPE apparatus (not shown) to grow a GaN layer 3 (FIG. 1C). In this growth, first, after reducing the pressure in the MOVPE apparatus by evacuation (for example, 5 × 10 ⁻² Torr), hydrogen is introduced into the apparatus and the pressure is returned to the atmospheric pressure to thereby return the atmosphere in the MOVPE apparatus. Was cleaned.

Thereafter, the temperature of the sapphire substrate 1 was raised to 1100 ° C. in an atmosphere containing ammonia (NH ₃ : for example, 20 slm), hydrogen (for example, 30 slm), and nitrogen (for example, 50 slm). When the temperature of the sapphire substrate 1 reached 1100 ° C., trimethylgallium (TMG) began to flow at a predetermined flow rate (for example, 846 μmol / min), and the GaN layer 3 was grown. Then, TMG was stopped and GaN growth was completed.

  Thereafter, the substrate temperature was lowered to room temperature, and the sapphire substrate 1 was taken out from the MOVPE apparatus. The conditions after the start of the growth of the GaN layer 3 were the same as those in the above-described two-stage growth method.

  As shown in FIG. 2 (b), the time required for the MOVPE growth is 2 hours in total: from room temperature to 1100 ° C. (30 minutes) → GaN growth (60 minutes) → down to room temperature (30 minutes). This was significantly shorter than 3 hours or more of the step growth method.

  The reason for raising the temperature from room temperature shown in FIG. 2B in an atmosphere containing ammonia, hydrogen, and nitrogen is to prevent the growth state of the surface modification layer 2 from fluctuating greatly from growth to growth. is there. When the temperature was raised in the same manner as in the two-step growth method, the characteristics of the obtained GaN layer 2 varied greatly with each growth. Therefore, when the cause of this instability was investigated, a sapphire substrate 1 having a nitrided surface was introduced into a growth apparatus, and while the temperature was raised from room temperature to the growth temperature (about 1100 ° C.), a normal MOVPE growth atmosphere was obtained. It has been found that the thickness of the surface modification layer 2 is changed for each growth by etching the surface modification layer 2 on the surface of the sapphire substrate 1 with the existing hydrogen.

Therefore, as a measure for preventing the etching of the surface modification layer 2,
(1) Raise the temperature in ammonia (2) Considering raising the temperature in an inert gas such as nitrogen (or in an inert gas with a low hydrogen concentration), the stability of growth is greatly improved by either method It turns out that it can improve. Specifically, the variation from the average value of the thickness and the X-ray diffraction half-value width of the obtained GaN layer 3 was ± 3% or less, which was significantly improved from the value obtained by the conventional method (± 20%). Furthermore, the average value of the thickness and the half width of the X-ray diffraction is almost the same value as the GaN layer 105 by the two-stage growth method, or rather improved, and the film quality is equal to or better than the GaN layer 105 by the two-stage growth method The GaN layer 3 was able to grow more stably.

  FIG. 3 shows the thickness characteristics of the GaN layer when GaN growth is performed 100 times under the same conditions, and FIG. 4 shows the X-ray diffraction half-width characteristics of the GaN layers when GaN growth is performed 100 times under the same conditions. Show.

  3 and 4 according to the present embodiment and the characteristics of the conventional two-stage growth shown in FIGS. 7 and 8 are clearly compared, and the characteristics of FIGS. It can be seen that the fluctuation is small (± 2% or less with respect to the average value). Further, the average value of the thickness of the GaN layer is 1.84 μm, and the average value of the X-ray half width is 265 seconds. From this, the GaN layer growth method according to the present embodiment has an increased growth rate (that is, improved production efficiency) and an X-ray diffraction half width compared to the case of two-stage growth (1.5 μm, 329 seconds). (Ie, a reduction in dislocations).

  In the above embodiment, the plasma is preferably generated by any of a parallel plate plasma apparatus, an ECR plasma apparatus, and an ICP plasma apparatus.

  The plasma is preferably a gas plasma containing nitrogen atoms, and the surface modification layer 2 is preferably a nitride layer.

In the present embodiment, the plasma is a plasma of a mixed gas of a gas containing nitrogen atoms and a gas containing silicon atoms, and the surface modification layer 2 contains at least Al, N, Si, and O atoms. Configuration is also possible. In this case, a gas containing nitrogen atoms described above, N _2, NH _3, preferably at N ₂ either O, also, the gas containing the silicon _{atoms, SiH 4, Si 2 H 6} , SiF Any of ₄ is preferable.

  In the above embodiment, the growth temperature of the region in which the GaN layer 3 is grown at least in contact with the surface modification layer 2 is preferably 900 ° C. or higher.

  In the above embodiment, in the process of raising the temperature of the sapphire substrate 1 to the growth temperature of the GaN layer 3, ammonia is introduced into the vapor phase growth apparatus so that the temperature of the sapphire substrate 1 is 800 ° C. or less. It is preferable to start. The ammonia introduction start temperature is preferably 300 ° C. or lower, but may be 100 ° C. or lower.

  The atmosphere containing ammonia is preferably any one of a mixed gas of ammonia and hydrogen, a mixed gas of ammonia and nitrogen, or a mixed gas of ammonia, hydrogen and nitrogen.

  For vapor phase growth, hydride vapor phase epitaxy (HVPE) can be used instead of metal organic vapor phase epitaxy (MOVPE).

(Effects of the first embodiment)
According to the first embodiment, the following effects are obtained.
(1) Plasma nitriding the surface of the sapphire substrate 1 to form a surface modified layer 2, using the surface modified layer 2 as a nucleus serving as a starting point for crystal growth, and a GaN layer 3 formed thereon by vapor deposition By forming it, it is possible to overcome the low production efficiency and the instability of growth, which are the disadvantages of the two-stage growth method.
(2) When forming the GaN layer 3 on the surface modification layer 2 of the sapphire substrate 1 by vapor phase growth, the temperature of the sapphire substrate 1 is increased to the growth temperature of the GaN layer 3 by using ammonia. By carrying out in the atmosphere containing it, it becomes possible to prevent the surface modification layer 2 from fluctuating greatly at every growth, and the GaN layer 3 can be grown stably.
(4) By performing nitriding with a plasma CVD apparatus and performing vapor phase growth with a MOVPE apparatus, it becomes possible to perform nitriding and growth in parallel, and the production efficiency is determined by MOVPE growth with a long time. Since the plasma nitriding time does not affect the production efficiency, the production efficiency of the GaN layer 3 can be increased.

  In the above embodiment, the temperature raising step from room temperature to 1100 ° C. shown in FIG. 2B is performed in an atmosphere of an inert gas such as nitrogen or nitrogen instead of being performed in an atmosphere containing ammonia. Even in an atmosphere in which hydrogen having a concentration of 10% or less is mixed with this inert gas, the same effect as in the above embodiment can be obtained.

[Second Embodiment]
In the second embodiment, in the state where only nitrogen is flowed at a constant rate (for example, 100 slm), the temperature raising process of FIG. 1B is performed in the MOVPE apparatus, and the temperature of the sapphire substrate 1 is 1100 ° C. At this stage, as in the first embodiment, ammonia, hydrogen, and nitrogen were introduced into the MOVPE apparatus, and TMG flow (for example, 846 μmol / min) was started to start GaN growth. The others are the same as those in the first embodiment.

  According to the second embodiment, the variation in the thickness and the X-ray half width of the GaN layer 3 is slightly larger (about ± 3%) than in the first embodiment, but in the case of the conventional two-stage growth The stability of growth could be remarkably improved from ± 20%. Moreover, the average value of the thickness of the GaN layer 3 grown under the above growth conditions was 1.7 μm, and the X-ray diffraction half-width was 282 seconds. The same results as in the first embodiment were obtained. .

  The average value of the X-ray half width is 265 seconds in the first embodiment and 282 seconds in the second embodiment. When a light emitting diode is manufactured using these, the conventional two-stage growth is achieved. An optical output equivalent to or better than that used was obtained. From this, it can be seen that the X-ray half width of the GaN layer manufactured by this method is preferably 290 seconds or less.

[Third Embodiment]
In the first embodiment, a gas introduced into the plasma apparatus when plasma is generated is selected from the following (1) and (2) one by one, and each gas is mixed at a ratio of 1: 1 (total of six types). As a result, plasma treatment and growth were performed in accordance with the steps shown in FIG.
(1) N ₂ , NH ₃ , N ₂ O
(2) SiH ₄ , Si ₂ H ₆ , SiF ₄

  In this case, the variation of the average value of the X-ray half width was about 5%, which was larger than that of the first embodiment, but almost the same result as that of the above embodiment was obtained. In this case, the modified state of the sapphire surface is not a simple nitridation as in each of the above embodiments, but is modified to a material in which A1, N, Si, and O that incorporate Si in the gas are mixed. Therefore, it is considered that a result slightly different from the above embodiments was obtained. However, even when Si is mixed in this way, the stability of growth is significantly improved as compared with the conventional two-stage growth method.

[Fourth Embodiment]
The fourth embodiment is obtained by slightly changing only the temperature raising process in the first embodiment. That is, the gas flowing in the MOVPE apparatus is, for example, hydrogen 50 slm and nitrogen 50 slm in the first stage of the temperature raising process, and further, when the temperature reaches a certain temperature T, for example, ammonia 20 slm, hydrogen 30 slm, nitrogen The temperature was raised to 1100 ° C. while changing to 50 slm.

  When a certain temperature T was 100 ° C. or lower, the same result as in the first embodiment was obtained. Moreover, when a certain temperature T is 100 to 300 ° C. or less, the thickness of the GaN layer 3 and the average value of the X-ray diffraction half-value width are approximately the same as those in the first embodiment. Although it is slightly larger than the embodiment of the present invention and is about ± 3%, it is much smaller than the conventional two-stage growth method.

  Moreover, when a certain temperature T is between 300 and 800 ° C., the thickness of the GaN layer 3 and the average value of the X-ray diffraction half width deteriorated to the same extent as that by the two-step growth method. However, those fluctuations were ± 20% or less, and higher growth reproducibility was obtained than in the two-stage growth method.

  In addition, when a certain temperature T is 800 ° C. or higher, the average value of the thickness of the GaN layer 3 and the X-ray diffraction half width is worse than that of the two-step growth method, and the fluctuation is two-step growth of ± 30% or more. It became larger than the case by law. This is because the surface modification layer 2 was etched by hydrogen in the atmosphere as described above.

Next, Examples 1 to 3 of the present invention will be described.
Example 1
In the first embodiment, only the temperature raising process was slightly changed. That is, the gas to be flowed during the temperature rise is the following (3) ammonia 20 slm, hydrogen 80 slm,
(4) Or ammonia 20 slm, nitrogen 80 slm,
Went as. As a result, the same result as in the first embodiment was obtained.

(Example 2)
In this example, the GaN layer 3 is grown using an HVPE (hydride vapor phase epitaxy) apparatus in the first embodiment. A specific growth procedure of this embodiment will be described below.

After introducing the sapphire substrate 1 having been subjected to the nitriding treatment into the HVPE apparatus, the inside of the HVPE apparatus was decompressed to 5 × 10 ⁻¹ Torr by evacuation. Thereafter, hydrogen was introduced into the HVPE apparatus and the pressure was returned to atmospheric pressure to clean the inside of the HVPE apparatus.

  Thereafter, ammonia 2 slm, hydrogen 3 slm, and nitrogen 5 slm were introduced into the HVPE apparatus, and the temperature of the sapphire substrate 1 was raised to 1100 ° C. as shown in FIG. When the temperature of the sapphire substrate 1 reached 1100 ° C., the growth of the GaN layer 3 was started by introducing 500 ccm of GaCl gas generated by spraying HCl onto metal Ga kept at 800 ° C. The growth time was 30 minutes. After 30 minutes, the supply of GaCl was stopped and the growth was completed. Thereafter, the temperature of the sapphire substrate 1 was lowered to room temperature, and the sapphire substrate 1 was taken out. As a result, the same result as in the first embodiment was obtained.

(Example 3)
In this example, in the second embodiment, the GaN layer 3 was grown by the HVPE apparatus and the following growth procedure was used.

First, after the sapphire substrate 1 subjected to nitriding treatment is introduced into the HVPE apparatus, the inside of the HVPE apparatus is reduced to 5 × 10 ⁻¹ Torr by evacuation, and then nitrogen is introduced into the HVPE apparatus to increase the pressure. The atmosphere in the HVPE apparatus was cleaned by returning to atmospheric pressure.

  Thereafter, the nitrogen flow rate was set to 10 slm, and the temperature of the sapphire substrate 1 was raised to 1100 ° C. When the substrate temperature reaches 1100 ° C., the gas flowing into the HVPE apparatus is ammonia 2 slm, hydrogen 3 slm, nitrogen 5 slm, and further 500 ccm of GaCl gas generated by spraying HCl on metal Ga maintained at 800 ° C. is introduced. GaN growth started. The growth time was 30 minutes. After 30 minutes, the supply of GaCl was stopped and the growth was completed. Thereafter, the substrate temperature was lowered to room temperature, and the sapphire substrate 1 was taken out. According to the present example, the same result as in the second embodiment was obtained.

[Other embodiments]
The present invention is not limited to the above embodiments, and various modifications can be made without departing from or changing the technical idea of the present invention.

  For example, in each of the above embodiments, a parallel plate plasma device or an ICP plasma device can be used in place of the ECR plasma device when forming the surface modification layer 2.

Further, ammonia or N ₂ O can be used as the gas introduced when forming the surface modification layer 2 instead of [ammonia + hydrogen + nitrogen]. Thereby, this invention can form the surface modification layer 2 irrespective of the gas kind to be used.

  In each of the above embodiments, the growth start by the MOVPE method (that is, the introduction of TMG) is started during the temperature rise before the temperature reaches 1100 ° C., and the temperature is raised to 1100 ° C. while growing. A temperature sequence up to is also possible. In this case, if the growth start temperature is 900 ° C. or higher, the same result as in the above embodiments can be obtained.

1 Sapphire substrate 2 Surface modification layer (nitriding layer)
3 GaN layer 101 Sapphire substrate 102 Hydrogen gas 103 Low temperature growth buffer layer 104 Single crystal nucleus 105 GaN layer

Claims (11)

First, the sapphire substrate is heated to a temperature at which a nitride layer formed by nitriding the surface of the sapphire substrate on the sapphire substrate is formed by plasma irradiation, and the nitride layer is formed by the plasma irradiation . And the process of
A second step of raising the temperature of the sapphire substrate on which the nitride layer has been formed to the growth temperature of a nitride semiconductor in an atmosphere of an inert gas or an atmosphere in which an inert gas is mixed with hydrogen having a concentration of 10% or less. When,
And a third step of growing a nitride semiconductor layer on the surface of the nitride layer.   The nitride semiconductor manufacturing method according to claim 1, wherein the nitride layer has a thickness in a range of 1 to 10 nm.   2. The method of manufacturing a nitride semiconductor according to claim 1, wherein in the first step, the plasma is generated using any one of a parallel plate plasma device, an electron cyclotron resonance (ECR) plasma device, and an inductively coupled (ICP) plasma device. Method.   The method of manufacturing a nitride semiconductor according to claim 1, wherein the plasma is a plasma of a gas containing nitrogen atoms. The method for producing a nitride semiconductor according to claim 4, wherein the gas containing nitrogen atoms is any one of N ₂ , NH ₃ , and N ₂ O. The nitride layer includes at least Al, N, Si, and O atoms,
2. The method for producing a nitride semiconductor according to claim 1, wherein the plasma is a plasma of a mixed gas of a gas containing nitrogen atoms and a gas containing silicon atoms. The method for manufacturing a nitride semiconductor according to claim ₆ , wherein the gas containing silicon atoms is any one of SiH ₄ , Si ₂ H ₆ , and SiF ₄ .   The method for manufacturing a nitride semiconductor according to claim 1, wherein the inert gas contains nitrogen.   2. The method for manufacturing a nitride semiconductor according to claim 1, wherein in the third step, a growth temperature of a region of the nitride semiconductor layer grown in contact with the nitride layer is set to 900 ° C. or higher.   2. The method for producing a nitride semiconductor according to claim 1, wherein in the third step, the nitride semiconductor layer is grown by metal organic vapor phase epitaxy or hydride vapor phase epitaxy. The third step is such that an average value of X-ray diffraction half-widths of the nitride semiconductor layer when the growth of the nitride semiconductor layer is performed 100 times under the same conditions is 290 seconds or less. A method for producing a nitride semiconductor as described in 1.

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