JP2009120465A - Semi-insulating nitride semiconductor substrate and method of manufacturing the same, nitride semiconductor epitaxial substrate and field-effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semi-insulating nitride semiconductor crystal substrate with less warpage and free from cracking, and to provide a method for manufacturing the substrate. <P>SOLUTION: A mask in which dotted or striped coating portions having a width or a diameter s from 10 μm to 100 μm are arranged at an interval w from 250 μm to 2,000 μm is formed on an underlying substrate. A nitride semiconductor crystal is grown on the underlying substrate by an HVPE method at a growth temperature from 1,040°C to 1,150°C by supplying a group III raw material gas and a group V raw material gas having a V/III group ratio b of 1 to 10, and a gas containing iron, and removing the underlying substrate to thereby obtain a free-standing semi-insulating nitride semiconductor substrate having a resistivity of not less than 1×10<SP>5</SP>Ωcm, a thickness of not less than 100 μm and a radius of curvature in the warpage of not less than 3 m. Further, a method of manufacturing a device using the above substrate is obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

   The present invention relates to a semi-insulating nitride semiconductor substrate, a manufacturing method thereof, a nitride semiconductor epitaxial substrate, and a field effect transistor. A nitride semiconductor refers to gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN) and mixed crystals of InGaN, AlInGaN, and the like. The target is not a thin film attached on the base substrate but a self-supporting crystal substrate. Here, GaN is mainly described. Since gallium nitride (GaN) has a wide band gap, it is used as a material for blue light-emitting elements.

Conventionally, light emitting devices such as blue light emitting diodes and semiconductor lasers have been manufactured by epitaxially growing nitride semiconductor thin film crystals such as InGaN, GaN, and AlInGaN on a sapphire single crystal substrate (α-Al ₂ O ₃ ). . Sapphire is the same hexagonal system as gallium nitride. A GaN C-plane thin film is grown on the sapphire C-plane crystal.

  However, since the sapphire substrate is insulative and the n-electrode cannot be taken from the bottom surface, and the cleavage surface of the GaN and the cleavage surface of the sapphire substrate are different, it must be separated by a cutting machine, which takes time and effort. There is a drawback that the yield of chip separation is poor.

  Also, the lattice constants of gallium nitride (GaN) and sapphire are quite different. GaN grown on a sapphire substrate has a large dislocation density. The warpage is also large. Therefore, in order to use gallium nitride itself as a substrate, an attempt was made to produce a substrate crystal with gallium nitride. Gallium nitride has been considered as a suitable material for blue light-emitting elements because of its wide band gap. In the case of a light-emitting element, it is convenient to take an n-electrode on the bottom and a p-electrode on the apex, so that a highly conductive substrate is desired.

In the manufacture of nitride semiconductor substrates, the growth of n-type nitride semiconductor crystals having a high free electron density has been aimed at. Currently, it is possible to produce n-type GaN free-standing substrates having a diameter of 2 inches. The present invention relates to the growth of nitride semiconductors that are semi-insulating rather than n-type.

  In addition to having a wide band gap, GaN has excellent characteristics when used as an electronic device. For example, currently Si is mostly used as a material for field effect transistors (FETs). However, GaN semiconductors are considered to be superior to Si semiconductors in terms of electron mobility and withstand voltage characteristics. The electron mobility of GaN is higher than that of Si, and the breakdown voltage is higher than that of Si. If an FET can be made of GaN, there is a possibility that it will be a high-current, high-voltage FET that is faster than Si. It is said that if a junction such as AlGaN / GaN is made, a two-dimensional electron gas will still be generated at the AlGaN / GaN boundary. Two-dimensional electron gas will run at high speed.

  The present invention aims to manufacture a nitride semiconductor crystal as a material for an FET, not as a material for an optical element as in the prior art.

  If an FET using a GaN / AlGaN thin film is made, it will be made on a sapphire substrate at first. In the FET, drain, gate and source electrodes are formed close to each other on the semiconductor layer, and current flows horizontally. A source, gate, and drain electrode may be provided side by side on the top surface. This is different from the case of a light emitting element that flows in the vertical direction in the substrate.

  In the case of an FET, an insulating sapphire substrate may be used because there is no problem of the back surface n electrode, but the problem of lattice mismatch still remains. Furthermore, due to cost problems, GaN FETs are still far from practical use.

  However, if a GaN-FET is to be made, it is better to use a GaN crystal substrate rather than a sapphire substrate and form an epitaxial thin film such as GaN or AlGaN on the GaN substrate rather than a sapphire substrate.

  Since it is a substrate for an FET, an insulating material having a high resistance is desired instead of a highly conductive n-type. This is very different from the properties required for the conventional GaN crystal substrates for light emitting devices. The present invention relates to a method for producing an insulating GaN substrate crystal that can be used as an FET substrate.

  First, the dopant will be described. Conventionally, GaN and InGaN thin films have been used for blue light emitting devices. To make it p-type, Mg or Zn is doped. To make it n-type, Si is doped. The inventors of the present invention first found out that oxygen may be doped to form an n-type GaN substrate. Therefore, n-type dopants are Si and O. Then, what is used as a dopant for making the GaN crystal insulative and under what conditions? There is a problem.

When a nitride semiconductor thin film (GaN, InGaN, AlGaN thin film) is formed on a sapphire substrate in order to manufacture a light emitting element, the MOCVD method is often used. Since it is a gas phase synthesis method, the raw material is given in a gaseous form. Nitrogen is provided in the form of ammonia (NH ₃ ). The MOCVD process gives Group 3 elements in the form of organometallics. A group 3 element organic metal such as gallium or indium (trimethylgallium, triethylindium or the like) and NH ₃ are used as raw materials and supplied onto a heated sapphire substrate.

  The HVPE method is often used to produce a GaN-based semiconductor thin film by a vapor phase synthesis method. In this method, a Ga boat containing a Ga metal melt is provided on a susceptor, and HCl is blown to synthesize GaCl, which is used as a Ga raw material. Accordingly, the source gases are GaCl and ammonia.

As a matter of dopant, iron (Fe) is doped to make GaN insulative. Iron (Fe) forms deep levels in the band gap of GaN and captures n-type carriers (free electrons), so that the number of carriers decreases. For this reason, the GaN crystal becomes semi-insulating. It is called semi-insulating (SI-GaN) because it is not completely insulating, but it has such a high resistivity that it can be used as a substrate for an FET. Since it is added to the inside of the vapor-grown nitride semiconductor, it is necessary to use a gaseous iron compound. For example, biscyclopentadienyl iron ((C ₅ H ₅ ) ₂ Fe), bismethylcyclopentadienyl iron ((CH ₃ C ₅ H ₄ ) ₂ Fe), or the like is used.

  In Patent Document 1, a GaN buffer layer is formed on a GaAs substrate with a window diameter of 1 to 5 μm and a window pitch of 4 μm to 10 μm, and GaN is formed thereon by MOCVD at 820 ° C. or 970 ° C. Alternatively, a technique is described in which a thick GaN crystal is obtained by C-plane growth by HVPE at 970 ° C., 1000 ° C., 1010 ° C., 1020 ° C., and 1030 ° C.

  Patent Document 1 uses a mask having a fine window. FIG. 1 shows a plan view of an example of a mask. A mask in which a large number of small windows W are regularly arranged in a wide covering portion M. The base substrate U is exposed from the window W. The area of the covering portion M is larger than that of the opening (window W).

  The principle of dislocation reduction by the mask method will be described with reference to FIG. 2 (1) to 2 (7) are cross-sectional views showing the state of crystal growth by the mask method. As shown in FIG. 2A, the mask M is a mask material formed on the base substrate U and provided with small windows W regularly. When gallium nitride is vapor-phase grown, a gallium nitride crystal G is formed only in the window W. Many upward dislocations T are generated at the boundary between the crystal G and the base substrate U (FIG. 2B).

  As the growth proceeds, a part of the crystal on the window W rides on the mask M and extends laterally on the mask (FIG. 2 (3)). Since it grows in the horizontal direction, the dislocation T also extends in the horizontal direction. The lateral surface is facet F with a low index. As shown in FIG. 2 (4), the crystal G extends in the upward and lateral directions and has a truncated cone shape. The upper surface of the table is a C surface (C). As shown in FIG. 2 (5), crystals extending from adjacent windows come into contact. The dislocation T stretches sideways and collides with the dislocation T. As a result, the dislocations cancel each other.

  As shown in FIG. 2 (6), the groove of the facet F is filled and becomes smaller. Eventually, the concave portion formed by the facet is filled to form a flat surface C. The flat surface is a C plane. Thereafter, the growth is continued with the flat C-plane as the surface. The dislocation T is large on the window W and small on the mask M.

  Patent Document 1 is an important conventional technique because the growth temperature, the raw material partial pressure, and the like are specifically shown. Reference 1 describes the growth temperature as follows. In the case of the HVPE method, the growth temperature is 970 ° C., 1000 ° C., 1010 ° C., 1020 ° C., 1030 ° C. In the case of the MOCVD method, the growth temperatures are 820 ° C. and 970 ° C.

In the HVPE method, the raw materials are HCl, Ga melt, and NH ₃ . The Group 3 raw material is made GaCl by reacting Ga melt with HCl gas. The amount of the Group 3 material and the Group 5 material to be supplied is expressed by the partial pressure P _{GaCl of GaCl} and the partial pressure P _{NH3 of} NH ₃ . The ratio b of the Group 3 and Group 5 materials can be expressed by the ratio of the NH ₃ partial pressure P _{NH 3} and the GaCl partial pressure P _GaCl . That is, it is defined as b = P _NH3 / P _GaCl .

  The specific resistance r of the GaN crystal produced by the mask method is assumed to be in the range of r = 0.005 Ωcm to 0.08 Ωcm.

  The growth conditions by the MOCVD method described in the example of Patent Document 1 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , TMG partial pressure P _TMG , and _5/3 group ratio b are shown in this order.
970 ° C 20 kPa 0.2 kPa 100 times
970 ° C 25 kPa 0.2 kPa 100 times
820 ° C 20 kPa 0.3 kPa 67 times
970 ° C 20 kPa 0.2 kPa 100 times
1000 ° C 20 kPa 0.4 kPa 50 times
970 ° C 25 kPa 0.5 kPa 50 times

  The growth conditions by the HVPE method described in the example of Patent Document 1 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , HCl partial pressure P _HCl , and _5/3 group ratio b are shown in this order.
970 ° C 25kPa 2kPa 12.5 times
970 ° C 25 kPa 2.5 kPa 10 times
970 ° C 25 kPa 0.5 kPa 50 times 1000 ° C 20 kPa 2 kPa 10 times
950 ° C 25kPa 2kPa 12.5 times
1020 ° C 25kPa 2kPa 12.5 times
1000 ° C 25 kPa 2 kPa 12.5 times 1010 ° C 25 kPa 2 kPa 12.5 times 1030 ° C 25 kPa 2 kPa 12.5 times

  In Patent Document 2, a mask having fine windows in a staggered pattern is formed on a GaAs substrate, and GaN is grown thickly while maintaining the C plane by the HVPE method, and the GaAs substrate is removed to have a diameter of 20 mm or more. A self-standing GaN substrate having a thickness of 70 μm or more and a deflection (warpage) of 0.55 mm or less in terms of a diameter of 50 mm is provided. A 50 mm diameter wafer having a center deflection (warp) of 0.55 mm is approximately 600 mm = 0.6 m in terms of the radius of curvature R.

In Patent Document 2, the growth temperature is 970 ° C., 1020 ° C., 1030 ° C. by HVPE method, GaCl partial pressure P _GaCl is 1 kPa or 2 kPa (0.01-0.02 atm), and NH ₃ partial pressure is 4 kPa or 6 kPa. . It is stated that when the GaCl partial pressure is P _GaCl = 1 kPa, the surface is flat but the warpage is large, the internal stress is huge, the crystal is easy to crack and cannot be used, and the film thickness cannot be 70 μm or more.

On the contrary, when the GaCl partial pressure is set to P _GaCl = 2 kPa, the surface is rough, but it is described that a crystal with small warpage and small internal stress is formed. NH ₃ partial pressures are 6 kPa, 12 kPa, and 24 kPa. The 5/3 group ratio b is b = 3, 6, 12. The radius of curvature is about 1 m. The specific resistance is 0.0035 to 0.0083 Ωcm. It is an n-type crystal.

  The growth conditions described in the example of Patent Document 2 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , GaCl partial pressure P _GaCl , and _5/3 group ratio b are shown in this order.
1030 ° C 4kPa 1kPa 4 times
1030 ℃ 6kPa 1kPa 6 times
970 ℃ 6kPa 2kPa 3 times
970 ° C 6kPa 1kPa 6 times
970 ° C 6kPa 1kPa 6 times
1020 ° C 6 kPa 2 kPa 3 times
1020 ° C 6 kPa 2 kPa 3 times
1030 ℃ 6kPa 1kPa 6 times
970 ℃ 6kPa 2kPa 3 times
970 ° C 12kPa 2kPa 6 times
970 ° C 24kPa 2kPa 12 times

  Patent Document 3 discloses a mask having dotted windows arranged on a GaAs substrate at regular intervals in the [11-2] direction and shifted by a half pitch in the [−110] direction, or a stripe extending in the [11-2] direction. A mask having a window or a mask having a stripe-like window extending in the [−110] direction is formed, a buffer layer is provided, GaN is epitaxially grown by HVPE while holding the C plane, and the substrate and the mask are removed. A method for manufacturing a self-standing single crystal substrate is proposed.

Patent Document 3 is also a method of reducing dislocations by forming a mask having a large number of small windows arranged vertically and horizontally on a base substrate U as shown in FIG. GaCl partial pressure _{P GaCl was} in some cases 1kPa two (0.01 atm) and 2 kPa (0.02 atm). In the case of 1 kPa, it is stated that a GaN crystal having a flat surface but large internal stress, large warpage, and easy cracking can be obtained. In the case of 2 kPa, it is stated that the surface is rough, and a GaN crystal having a small internal stress and a small warp and hardly cracked can be formed.

  It is said that when the growth temperature is 1020 ° C. or 1030 ° C., the surface is flat and the internal stress is large and cracks easily.

In the case of a thick crystal with a GaCl partial pressure of 2 kPa at a growth temperature of 970 ° C., it is said that a GaN crystal having a rough surface with small internal stress and small warpage can be formed. The NH ₃ partial pressure P _NH3 is 6 kPa to 12 kPa.

In summary, in Patent Document 3, the temperature for manufacturing a rough GaN crystal which is warped and has low internal stress and is difficult to crack is 970 ° C., GaCl partial pressure is 2 kPa, NH ₃ partial pressure is 6 to 12 kPa, and 5/3 group ratio. b is about 3-6. The specific resistance is 0.01 Ωcm to 0.017 Ωcm and is n-type.

  The HVPE growth conditions described in the example of Patent Document 3 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , GaCl partial pressure P _GaCl , and _5/3 group ratio b are shown in this order.
1030 ° C 4kPa 1kPa 4 times
1030 ℃ 6kPa 1kPa 6 times
970 ℃ 6kPa 2kPa 3 times
970 ° C 6kPa 1kPa 6 times
970 ° C 6kPa 1kPa 6 times
1020 ° C 6 kPa 2 kPa 3 times
1020 ° C 6 kPa 2 kPa 3 times
1030 ℃ 6kPa 1kPa 6 times
970 ℃ 6kPa 2kPa 3 times
970 ° C 12kPa 2kPa 6 times
970 ° C 24kPa 2kPa 12 times

  In Patent Document 4, double and triple ELO masks (Epitaxial Lateral Overgrowth) are alternately provided so as to reduce dislocations, while maintaining the C-plane of Si-doped n-type GaN crystals by MOCVD and HVPE. Grow. Since the ELO mask has a large dislocation density at the window and a small dislocation density on the mask, the dislocation density can be reduced by attaching double or triple ELO masks so that the windows are different. In the case of the MOCVD method, it is stated that the 5/3 group ratio b is 30 to 2000 times as a good condition.

In the embodiment, the raw material gas having a ratio of 5/3 group ratio b = 1200 times, 2222 times, 1800 times, 1500 times, 800 times, and 30 times is used. HVPE is not mentioned. The n-type dopant is Si. Silane gas (SiH ₄ ) is used for doping. First, a trapezoidal crystal is formed on the window of the ELO mask by the MOCVD method, and the HVPE method is switched immediately before being merged on the ELO mask. The preferred growth temperature is stated as 950 ° C. to 1050 ° C.

Patent Document 5 is almost the same as Patent Document 4, and proposes a device for reducing dislocations by using a double or triple ELO mask.
Patent Document 6 proposes for the first time a method for producing an n-type GaN substrate by doping GaN with oxygen as an n-type dopant.

In Patent Documents 4 and 5, silane gas (SiH ₄ ) is used to dope the crystal with Si as an n-type dopant. Silane gas may explode and is dangerous to use in large quantities for n-type substrate growth. Patent Document 6 has found that oxygen creates a shallow donor level in GaN. When water is added to the source gases NH ₃ , HCl, etc., an ELO mask is provided on the GaAs substrate and a GaN crystal is grown by the HVPE method, the C plane grows. However, oxygen is taken in from the source and the donor level is increased. An n-type carrier is generated to make the crystal n-type. Moreover, the activation rate is 100% over a wide concentration range. For the first time it has been shown that oxygen is a convenient n-type dopant for thick crystals such as substrates.

  Patent Document 7 reveals that there is significant anisotropy when oxygen is doped into GaN. The selectivity is such that oxygen hardly enters through the C plane ((0001) plane) and oxygen easily enters through a plane other than the C plane. In Patent Document 7, as shown in FIG. 17, on the surface, a large amount of non-C-faceted facets F that are grown in the c-axis direction on the average are produced, and oxygen is taken into the crystal through facets F that are non-C-planes Alternatively, as shown in FIG. 18, a method of doping oxygen from the non-C surface using a GaN base substrate having a non-C surface (hkmn) (≠ (0001) surface) has been proposed. Patent Document 7 reveals the remarkable anisotropy of oxygen doping for the first time.

  The HVPE growth conditions described in the example of Patent Document 7 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , HCl partial pressure P _HCl , and _5/3 group ratio b are shown in this order.
1020 ° C 20 kPa 1 kPa 20 times

  Patent Document 8 proposes a new dislocation density reduction method that is completely different from the ELO method. In Patent Document 8, by appropriately controlling the growth conditions, a large number of facets F and large and small pits P made of facets are actively created as shown in FIG. 3, and the facets F and pits P are not embedded and maintained until the end of growth. This is called facet growth because the facet is maintained until the end without being embedded. The pit P is a hexagonal pyramid or a 12-sided pyramid.

  As shown in the perspective view of the pit P in FIG. 4 and the plan view of the pit P in FIG. 5, when growing while maintaining the concave portion (pit P) of the facet F, a crystal is formed in the normal direction V of the facet F inside the pit P. grow up.

Since the dislocation T extends along the growth direction V, the dislocation T extends in the facet normal direction. The dislocation T is drawn into the boundary line B by facet growth. A set of dislocations T is formed below the boundary line B (planar defect PD).

  As facet growth progresses, dislocations gather further to the bottom of pit P. A large portion of dislocations T (linear defect set: H) is formed at the bottom of the pit P. Even if the total amount of dislocations does not change so much, dislocations gather in the planar defects PD and linear defects H, so that the dislocation density in other portions decreases. Unlike the ELO method, this is effective from the middle to the end of growth. This is a completely new dislocation density reduction method. This is called the facet growth method.

  Since the method of Patent Document 8 does not know where the pits P (concave portions) can be formed, it is called a random facet and distinguished from the subsequent improved type. The resulting crystals have significant irregularities on the surface.

  The growth conditions described in the example of Patent Document 8 are as follows.

The growth temperature T, NH ₃ partial pressure P _NH3 , HCl partial pressure P _HCl , and _5/3 group ratio b are shown in this order.
1050 ° C 20 kPa 0.5 kPa 40 times
1000 ° C 30 kPa 2 kPa 15 times
1050 ° C 20 kPa 0.5 kPa 40 times
1020 ° C 20 kPa 1 kPa 20 times
1000 ° C 30 kPa 2 kPa 15 times
1000 ° C 40 kPa 3 kPa 13 times
980 ° C 40 kPa 4 kPa 10 times

  Patent Document 8 can be called a random facet method because the position where the facet pit is formed is controlled by chance. Since there is no local specificity, dislocations that have once gathered may re-discrete with growth. Since it is a substrate on which a device is formed, it is more convenient if the position where the facet pit can be formed can be designated in advance. If dislocations are confined and re-discrete can be eliminated, further reduction of dislocations can be achieved.

  In Patent Document 9, as shown in FIG. 6, a mask is formed on a base substrate U so as to regularly arrange isolated dot-shaped covering portions M. The portion where the base substrate U is exposed (exposed portion E) is much wider than the covering portion (mask portion) M. GaN is vapor grown on the masked underlying substrate U. Since the growth is delayed on the covering portion M, a recess (facet pit P) having the covering portion M as a bottom is formed.

  The facet growth using a dot mask will be described with reference to FIG. As shown in FIG. 9 (1), an isolated spot-shaped covering portion M is formed on the base substrate U. When gallium nitride is vapor-phase grown, a crystal G grows only on the exposed portion E of the base substrate as shown in FIG. It does not grow on the covering portion M. As shown in FIG. 9 (3), crystals accumulate on the exposed portion E. The inclined surface is a facet F with a low index. As shown in FIG. 9 (4), a faceted pit P having a hexagonal pyramid or a 12-sided pyramid having a covering portion M as a bottom and an inclined surface as a facet F is formed. As shown in FIG. 9 (5), crystals are also placed on the covering portion M. This is a closed defect gathering region H gathered at a high density of dislocations. Under the facet is a single crystal low dislocation associated region Z. The flat surface is the C surface (C). Below the C plane is a single crystal low dislocation residual region Y.

  As shown in the perspective view of the crystal in FIG. 7 and the plan view in FIG. 8, facet pits P made of facets F such as inverted conical petals are arranged vertically and horizontally on the crystal surface. A portion corresponding to the stem is a closed defect gathering region H where dislocations are concentrated. A portion corresponding to the root is a covering portion M. The flat surface is the C surface. The portion (Y) formed below the C plane is a low dislocation portion. The bottom (Z) of facet F is also a low dislocation part. In order to distinguish this from others, it may be called a dot type. This method is temporarily called a dot facet growth method.

  As described above, the facet pit P has an action of collecting the dislocations T on the facet F at the boundary line B and collecting them at the bottom of the pit. The pit bottom (above the covering portion M) becomes a closed defect gathering region H where dislocations are concentrated. Once disassembled, dislocations are not re-discrete. Therefore, it is called “closed”. The other portions are a single crystal low dislocation associated region Z (which can be formed under the facet) with few dislocations and a single crystal low dislocation residual region Y (which can be formed under the C plane). Z and Y are low dislocations.

  According to Patent Document 9, the concept of a closed defect gathering region H, a single crystal low dislocation associated region Z, and a single crystal low dislocation residual region Y was first generated. Even if it says a mask, a small window does not exist with a fine pitch like an ELO mask. A large-sized spot-like (circle, square, etc.) covering portion M (FIG. 6) is formed in a wide exposed portion.

  In the ELO mask, the exposed portion E (window W) is narrower than the covering portion M, the exposed portion E is small (diameter 1 to 2 μm), and the pitch is also small (2 μm to 6 μm).

  On the contrary, in the mask that is the basis of the facet pits of Patent Document 9, the exposed portion E is wider than the covering portion M. The coating diameter is quite large (diameter 20 μm to 100 μm). The top of the cover is the bottom of the facet pit. Faceted pits do not collect dislocations at the bottom, capture them, and release the dislocations again. There is a feature that a closed defect gathering region H is formed at the position of the mask, and low dislocation portions Z and Y are formed around it. Low dislocations Z and Y are formed on the exposed portion E without a mask. Z can be directly below the facet, and Y can be directly below the C-plane growth portion. Both Z and Y are single crystals and low dislocations. An HZY concentric structure is formed around the point mask. In ELO, the mask exposure portion E (window W) has high density dislocations (H) and the coating portion has low dislocations (Z, Y). The relationship is exactly the opposite.

  The growth conditions in the example of Patent Document 9 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , HCl partial pressure P _HCl , and _5/3 group ratio b are shown in this order.
1050 ° C 30 kPa 2 kPa 15 times
1030 ° C 30 kPa 2.5 kPa 12 times
1010 ° C 20 kPa 2.5 kPa 8 times
1030 ° C 25 kPa 2.5 kPa 10 times
1050 ° C 30 kPa 2.5 kPa 12 times
1030 ° C 25kPa 2kPa 12.5 times
1030 ° C 25kPa 2kPa 12.5 times

  In Patent Document 9, since the mask is formed in the form of isolated points (dots) that are regularly distributed, a closed defect gathering region H is formed on the dot, and a single crystal low dislocation associated region Z and a single crystal low dislocation residual region Y are formed around it. Can do. Since devices such as semiconductor lasers and light emitting diodes are formed thereon, it may be inconvenient if the closed defect gathering regions H are dispersed.

  Therefore, in Patent Document 10, as shown in FIG. 10, a mask having a covering portion M with parallel stripes at equal intervals is formed on a base substrate U, and GaN is facet grown thereon. The sum of the width s of the mask covering portion M and the width w of the exposed portion E is the pitch p (p = s + w). s is much smaller than w. GaN is grown on the underlying substrate U by vapor phase growth.

  As shown in a plan view in FIG. 11 and a perspective view in FIG. 12, a large number of parallel peaks and valleys having a flat top surface are obtained. A parallel crystal defect gathering region H is formed on the covering portion M, and a parallel low defect single crystal region Z and a C-plane growth region Y are formed on the exposed portion. A set of dislocations formed on the parallel mask is called a crystal defect collecting region H. The continuous growth under the adjacent facet is called a low defect single crystal region Z. A C-plane growth region Y may or may not be formed between adjacent low defect single crystal regions Z.

  In Patent Document 9, since a defect region H is formed on an isolated point-like mask, the word “closed” is given and emphasized. However, in the case of a stripe mask, since H is not closed, a crystal defect gathering region. Call it H. Since Z spreads and does not necessarily accompany H, it was named low defect single crystal region Z. Y may or may not be possible. Since it occurs along the C plane, it is called a C plane growth region Y.

  Depending on the growth method, the C-plane growth region Y may disappear. As shown in the plan view of FIG. 13 and the perspective view of FIG. Parallel crystal defect gathering regions H are formed on the covering portion M. This is a valley. A low-defect single crystal region Z parallel to the exposed portion adjacent thereto is formed. The Yamagata facets F and F are pointed and have no C-plane part. The C-plane growth region Y has disappeared. ... ZHZH ... structure.

  The stripe facet growth method will be described with reference to FIG.

  As shown in FIG. 15 (1), a plurality of parallel-line stripe covering portions M are formed on the base substrate U. When vapor phase growth of gallium nitride is performed, a crystal G grows only on the exposed portion E of the base substrate as shown in FIG. It does not grow on the covering portion M. As shown in FIG. 15 (3), the crystal G is stacked on the exposed portion E. The inclined surface is a facet F with a low index. The crystal G has a parallel island shape separated by a covering portion. As shown in FIG. 15 (4), V-grooves having parallel inclined surfaces with the covering portion M at the bottom and inclined in the opposite direction are formed in parallel. Opposing inclined surfaces are facets F and F having the same angle but opposite inclination directions. A flat surface between adjacent masks is a C surface (C).

  Eventually, crystals will also be placed on the covering portion M as shown in FIG. This is a crystal defect gathering region H in which dislocations gather at a high density. Furthermore, crystal growth proceeds as shown in FIG. The crystal defect gathering region H on the mask M extends upward with the size as it is. The parallel facets F, F are wider. Immediately below the facets F, F is a low defect single crystal region Z. The boundaries between the crystal defect gathering region H and the low defect single crystal region Z are the crystal grain boundaries K and K. The crystal grain boundaries K and K confine the dislocations in the crystal defect gathering region H.

  The flat surface in the middle of the mask is the C surface (C). Below the C plane is a C plane growth region Y. The C surface (C) becomes gradually narrower. The pitch of the crystals forming the stripe structure is equal to the mask pitch p. The mask pitch p is the sum of the mask width s and the exposed portion width w (p = s + w). When the crystal growth further proceeds, parallel crystals such as mountain ranges with the crystal defect gathering region H as the ridge and the C plane as the ridge as shown in FIG. The C-plane portion (C) that hits the summit becomes narrower. Immediately below the facet F is a low-defect single crystal region Z, and immediately below the C-plane is a C-plane growth region Y.

  In some cases, the crystal grows upward while maintaining this shape. Or it may look like a parallel mountain range with even sharper peaks. FIG. 16 (2) shows such a case. In this case, the C plane is eliminated. The C-plane growth region Y is also lost.

  According to Patent Document 10, a structure of ZHZYZHZYZH ... or a structure of ZHZHZH ... can be formed in parallel. Dislocations concentrate on the crystal defect gathering region H, and the low defect single crystal region Z and the C-plane growth region Y are single crystals and low dislocations.

  The method of Patent Document 10 can be called a stripe-type facet growth method because a mask is formed in parallel and a crystal defect assembly region H is formed in parallel. This is because the low-defect single crystal regions Z are arranged in a straight line, so that devices such as semiconductor lasers and light-emitting diodes can be easily produced.

  The facet growth method and the ELO method are completely different methods. The shape, dimensions, and action of the mask are also different. The ELO mask and the stripe mask in which the windows are distributed in a zigzag pattern can be clearly distinguished from each other in shape and size. The stripe mask has a width s of about 20 μm to 300 μm and a pitch p of about 100 μm to 2000 μm. For example, the width s of the stripe mask is 50 μm, and p = 500 μm pitch.

  In the dot-type and stripe-type facet growth methods, the dislocations are concentrated in the crystal defect gathering region H on the mask and surrounded by the crystal grain boundaries K, K, so the dislocations are not re-discrete. Z and Y adjacent to H become a single crystal with low dislocations. The part may be a part through which the current of the device passes.

  Since the GaN crystal has a cleavage plane in the {1-100} direction, a laser resonator mirror can be formed by natural cleavage. Since oxygen is doped to form an n-type, an electric current passes and an n-electrode can be formed on the bottom surface. In that respect, it is superior to sapphire substrates.

  ELO has a small exposed area and a high dislocation density above it, and a wide covering area and a low dislocation. On the other hand, the striped facet method has a wide exposed area and a low dislocation, and a narrow covering area. High density dislocations.

  The growth conditions in the example of Patent Document 10 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , HCl partial pressure P _HCl , and _5/3 group ratio b are shown in this order.
1050 ° C 30 kPa 2 kPa 15 times
1030 ° C 30 kPa 2.5 kPa 12 times
1050 ° C 30 kPa 2 kPa 15 times
1010 ° C 20 kPa 2.5 kPa 8 times
1030 ° C 25kPa 2kPa 12.5 times
1030 ° C 25 kPa 2.5 kPa 10 times

Patent Document 11 discloses a MOCVD method using H ₂ , TMG, and ammonia as source gases and (C ₅ H ₅ ) ₂ Fe as a dopant, or H ₂ , HCl, Ga melt, ammonia on a sapphire (0001) substrate. A method has been proposed in which an iron-doped GaN substrate is obtained by growing an iron-doped GaN crystal by the HVPE method using (C ₅ H ₅ ) ₂ Fe as a dopant.

  The growth conditions in the example (MOCVD method) of Patent Document 11 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , TMG partial pressure P _TMG , and _5/3 group ratio b are shown in this order.
1000 ° C 15 kPa 0.3 kPa 50 times

  The growth conditions in the example (HVPE method) of Patent Document 11 are as follows.

The growth temperature Tq, NH ₃ partial pressure P _NH3 , HCl partial pressure P _GaCl , and _5/3 group ratio b are shown in this order.
1000 ° C 15 kPa 0.3 kPa 50 times

International Publication WO99 / 23693 (International Application PCT / JP98 / 04908)

Japanese Patent No. 3788037 (Japanese Patent Application No. 10-171276, Japanese Patent Laid-Open No. 2000-012900)

Japanese Patent No. 3788041 (Japanese Patent Application No. 10-183446, Japanese Patent Laid-Open No. 2000-022212)

International Publication WO 98/47170 (International Application PCT / JP98 / 01640)

EPC Publication EP0942459 A1 (EPC Application No. 9891274.8)

Japanese Patent No. 3788104 (Japanese Patent Application Laid-Open No. 2000-044400, Japanese Patent Application No. 11-144151 / Claim of priority Japanese Patent Application No. 10-147716)

Japanese Patent No. 3826825 (Japanese Patent Application Laid-Open No. 2002-373864, Japanese Patent Application No. 2002-103723 / claim of priority Japanese Patent Application No. 2001-113873)

JP 2001-102307 (Japanese Patent Application No. 11-273882)

Japanese Patent No. 3864870 (Japanese Patent Application Laid-Open No. 2003-165799, Japanese Patent Application No. 2002-230925 / Japanese Patent Application No. 2001-284323)

Patent No. 3801125 (Japanese Patent Application Laid-Open No. 2003-183100, Japanese Patent Application No. 2002-269387 / Priority Claim Japanese Patent Application No. 2001-311018)

JP-A-2005-306723 (Japanese Patent Application No. 2005-075734 / Priority Claim Japanese Patent Application No. 2004-085372)

  What has been described so far is an n-type GaN substrate used as a substrate for blue light-emitting diodes and semiconductor lasers. Although an AlInGaN substrate containing a little Al or In has been attempted, it is for use as a substrate of a light emitting device. It is n-type, has high conductivity, and can pass a high-density current. The dopant may be silicon (Si) or oxygen (O).

  However, an object of the present invention is not a n-type but a semi-insulating (SI) GaN substrate crystal. It is an SI substrate for applications such as FETs, not n-substrates for light emitting elements.

  In the case of a light-emitting element, since a high-density current is passed through the substrate, there is a risk that deterioration will proceed from dislocation.

  In the case of a semi-insulating substrate (SI-GaN substrate) for a lateral electronic device, it is necessary to have a voltage resistance and a high resistance enough to withstand a high voltage and a large current. If the substrate has a high dislocation density, it causes a leakage current, which is not preferable. Since multiple layers of GaN, InGaN, and AlGaN thin films having a regular lattice structure are formed on the substrate, fewer dislocations are better. In the case of a semi-insulating substrate, it is strongly desired that the substrate has a high insulating property, low warpage, low dislocation density, and few cracks.

  Any of the GaN substrates mentioned in the prior art (Patent Documents 1 to 10) has a low resistivity.

  Patent Document 1 says that 0.005 to 0.08 Ωcm, and Patent Document 2 says 0.0035 to 0.0083 Ωcm. Patent Document 3 states that the GaN substrate is 0.01 to 0.017 Ωcm.

  Since these are not described as having n-type dopants, it is considered that group 5 vacancies have created a donor level or n-type dopant elements contained in the raw material gas have entered.

  Patent Document 4 does not specifically describe the resistivity. This intends to make a low resistance n-type GaN substrate with Si as a dopant. Therefore, it is estimated that the resistivity will be lower than those of Patent Documents 1 to 3. From these descriptions, it seems that the upper limit of the specific resistance of the conventional GaN crystal is about 0.08 Ωcm.

Such an insulating substrate as a substrate for a lateral electronic device does not help. The insulating group 3-5 nitride substrate is desired to have a specific resistance of 10 ⁵ Ωcm or more. Depending on the purpose, 10 ⁶ Ωcm or more or 10 ⁷ Ωcm or more may be required.

  Conventional GaN crystal manufacturing technology cannot produce such a high resistance crystal. What should i do? Since the group 5 vacancies become donors, the supply of group 5 can be increased to prevent this. As already described, the MOCVD method says that the 5/3 group ratio b is 1000 to 2000 times, and if the group 5 ratio is further increased, the waste of the raw material increases. In the case of HVPE, the 5/3 group ratio b is often about 12 to 50 times. Although it is possible to further increase the Group 5 raw material ratio, this is not preferable because it results in loss of raw materials.

  A high-resistance gallium nitride crystal could be made by using a high-purity raw material and preventing impurities from entering. However, even if it is natural, it becomes n-type and insulation which can be used for a lateral electronic device cannot be obtained.

  Another option is to suppress the movement of the n-type carrier by adding other elements. Patent Document 11 states that iron-doped GaN crystals are semi-insulating. Since it is a vapor phase growth method, it is necessary to give an iron compound in a gaseous state. In Patent Document 11, gallium nitride is produced by MOCVD on a sapphire substrate using biscyclopentadienyl iron as a dopant. In Patent Document 11, an iron-doped GaN crystal is grown on a sapphire substrate without using a mask.

  It is a novel finding that iron can increase the resistivity of GaN crystals. It has been found from Patent Document 11 that iron doping is an effective means for producing semi-insulating GaN. In addition, in order to use as a substrate for an electric element such as an FET, it is also important that the crack generation rate is low and the crack generation rate is low. Patent Document 11 does not describe the generation of cracks or cracks at all.

In the method for producing an iron-doped nitride semiconductor substrate of the present invention, a dot mask or a stripe mask is attached to a base substrate, the substrate temperature is set to 1040 ° C. to 1150 ° C., and the ratio of the Group 5 and Group 3 gas raw materials is further increased by HVPE. While supplying ammonia gas, Group 3 gas, and iron compound gas so that b is 1 to 10, a nitride semiconductor crystal is grown thickly on the base substrate with a mask, and the base substrate is removed to remove 100 μm or more. A self-supporting iron-doped semi-insulating nitride semiconductor crystal substrate having a thickness and a specific resistance of 1 × 10 ⁵ Ωcm or more is obtained.

  As the base substrate, a (111) plane GaAs wafer, a sapphire wafer, a SiC wafer, a GaN wafer, or the like can be used.

FIG. 19 shows a schematic longitudinal sectional view of the HVPE furnace. A heater 3 is provided outside the vertically long reactor 2. The heater 3 extends in the vertical direction and is divided into several parts, and can generate an arbitrary temperature distribution in the vertical direction. The reactor 2 has a hot wall. A Ga reservoir 4 in which Ga melt is stored is provided in the upper part of the reaction furnace 2. Below the reaction furnace 2 is a susceptor 5 supported on a rotary shaft that can be rotated and raised. A base substrate 6 is placed on the susceptor 5. The first source gas supply pipe 7 supplies hydrogen (H ₂ ) and hydrogen chloride (HCl) gas to the Ga reservoir 4. HCl and Ga react to form GaCl gas. This moves downward. The second source gas supply pipe 8 allows hydrogen (H ₂ ) and ammonia (NH ₃ ) gas to flow above the base substrate 6. GaCl and NH ₃ react to form GaN. The third source gas supply pipe 10 supplies a gas mixture of iron (Fe) and a carrier gas (H ₂ ) into the reaction furnace. The synthesized GaN is doped with iron. After the reaction, exhaust gas and unreacted gas are discharged from the gas discharge pipe 9.

As the iron, biscyclopentadienyl (C ₅ H ₅ ) ₂ Fe or bismethylcyclopentadienyl (CH ₃ C ₅ H ₄ ) ₂ Fe is used as a raw material. Since these are gaseous, they are blown into the reactor as gas from the upper gas flow path. These are thermally decomposed and taken into the crystal. Alternatively, it reacts with HCl to form FeCl, FeCl ₂ , or FeCl ₃ and then blown into the crystal.

The iron concentration Fe in the nitride semiconductor substrate thus fabricated is 1 × 10 ²⁰ cm ⁻³ ≧ Fe ≧ 1 × 10 ¹⁶ cm ⁻³ . The resistivity of the nitride semiconductor substrate is 1 × 10 ⁵ Ωcm or more.

_Masks, etc. SiO 2, SiON, SiN, AlN , Al 2 O 3. In the case of a stripe mask, the mask has a covering portion width s of 10 μm to 100 μm. The space | interval w of a coating part shall be 250 micrometers-2000 micrometers. The pitch p is p = s + w. The pitch is p = 260 μm to 2100 μm.

  In the case of a dot mask, the covering portion diameter s is 10 μm to 100 μm. The space | interval of a coating part shall be w = 250 micrometers-2000 micrometers. The pitch p is 260 μm to 2100 μm.

  When the substrate temperature is 1040 ° C. to 1080 ° C., a mountain-shaped crystal (type II) having a facet surface that is low at the mask position and high at the exposed portion grows (FIG. 20). A crystal defect gathering region H is formed on the mask, and a low defect single crystal region Z is formed immediately below the facet F near the mask in the exposed portion.

  FIG. 20 shows an ideal form consisting only of a mountain shape to emphasize the comparison with FIG. This is realized only in a special case with a stripe mask. This is not the case with dot masks due to geometric constraints. In both the dot mask and the stripe mask, a C plane is actually formed at the middle position of the mask (indicated by a broken line), and a C plane growth region Y is often formed below the C plane. Tension can be alleviated because of the structure in which different things such as H and Z or H, Z and Y are mixed.

  The type II in FIG. 20 has a facet F on the upper surface, and tends to absorb a large amount of oxygen through the facet F. Therefore, the effect of iron doping may be canceled by oxygen which is an n-type impurity. Then, it is necessary to increase the iron concentration, and the amount of impurities as a whole may increase.

  When the substrate temperature is higher, from 1080 ° C. to 1150 ° C., crystals having a uniform height (type I) grow (FIG. 21). The surface is a substantially flat C surface. This also writes an ideal form for emphasizing the comparison with FIG. Actually, the upper part of the mask M is often slightly recessed. This is because the crystal defect gathering region H is formed on the mask. On the exposed portion, a low defect single crystal region Z and a C-plane growth region Y are mixed. Stress can be relieved because of the structure in which different tissues alternate.

  Type I grows with little facet F and does not take up oxygen. Therefore, the effect of iron doping becomes remarkable. The impurity concentration as a whole can be reduced. Since there are few impurities, an internal stress is small and there exists an advantage that a crack does not enter easily. That is, the I type is an optimum structure as an iron-doped nitride semiconductor. In order to make type I, it is better that the 5/3 group ratio b is lower at a higher temperature. The 5/3 group ratio b is set to 1 to 10 at a high temperature of 1080 to 1150 ° C. Furthermore, when the temperature is set to 1090 ° C. to 1150 ° C. and the 5/3 group ratio b is set to about 1 to 5, it can be more surely made into the I type.

Crystals having a trapezoidal apex in which type I and type II are mixed can be formed at a substrate temperature of about 1080 ° C. (1070 ° C. to 1090 ° C.) with a 5/3 group ratio b = 1-10.
Although three cross-sectional views (FIGS. 20, 21, and 24) are shown, a phase transition in which the cross-sectional shape suddenly changes at a certain temperature does not occur, but continuously depending on the temperature and the 5/3 group ratio b. The cross-sectional shape changes. An ideal flat type as shown in FIG. 21 can be obtained at a temperature of 1140 to 1150 ° C. and a group 5/3 ratio b1 to b1. As the temperature decreases, the flat shape in FIG. 21 changes to the mountain shape in FIG. 20 as the 5/3 group ratio b increases.

  The substrate temperature of 1050 ° C. to 1150 ° C. is the higher growth temperature of the nitride semiconductor vapor phase growth method. I-type growth means that if the temperature is raised, even a large mask can be grown with a flat surface.

  It can be said that the 5/3 group ratio b is 1 to 10 is an extremely small limit in the vapor phase growth method of a nitride semiconductor. The idea of the present invention is to grow an iron-doped nitride semiconductor with a low 5/3 group ratio b and a high growth temperature.

  What are the values of the substrate temperature and the 5/3 group ratio b in the conventional examples so far? When citing and explaining patent documents, the growth temperature (substrate temperature) and the 5/3 group ratio b were mentioned.

  FIG. 22 shows the relationship between the growth temperature and the 5/3 group ratio b for easy understanding. The horizontal axis is the growth temperature (substrate temperature). The vertical axis represents the 5/3 group ratio b in logarithm. Black dots indicate the substrate temperature and the 5/3 group ratio b by the HVPE method in the conventional example. A black circle surrounded by a white circle is based on the conventional MOCVD method. The appended number indicates the number of the cited patent document. One point corresponds to one embodiment.

  For example, there are three black and white circles at 970 ° C. and 100 times, and there are numbers 1, 1, 1. That is, the three examples of the MOCVD method of Patent Document 1 were 970 ° C. and 100 times higher. Patent Document 1 has nine black circles showing examples of HVPE at temperatures between 950 ° C. and 1020 ° C.

  Since Patent Document 4 does not have a clear example, the MOCVD method has a temperature range of 960 ° C. to 1050 ° C., and the 5/3 group ratio b = 1000 times, 800 times, etc. .

  Regarding the type II of the present invention, the point of temperature 5/3 group ratio b is indicated by a white triangle. There are 14 points at a temperature of 1050 ° C. and a 5/3 group ratio b = 2.5. There is one 5/3 group ratio b = 5 at a temperature of 1050 ° C. There is one 5/3 group ratio b = 10 at a temperature of 1050 ° C.

  Regarding the type I of the present invention, the point of temperature 5/3 group ratio b is indicated by a white circle. There are 19 points at a temperature of 1110 ° C. and a 5/3 group ratio b = 2.5. There is one 5/3 group ratio b = 3 at a temperature of 1110 ° C. There is one point of 5/3 group ratio b = 1 at a temperature of 1110 ° C. and one point of 5/3 group ratio b = 2.5 at a temperature of 1100 ° C.

  The range of the temperature 5/3 group ratio b of the present invention is surrounded by a broken line. 1080 ° C. is an intermediate mixing type temperature.

  Patent Documents 2 and 3 do not use a mask with a large pitch. There are eight examples where the 5/3 group ratio b is 3. There are two examples where the 5/3 group ratio b is 4. There are ten examples where the 5/3 group ratio b is six. However, the substrate temperature is 970 ° C., 1020 ° C., 1030 ° C., which is 1040 ° C. or less which is the lower limit of the present invention. Patent Documents 2 and 3 do not use a wide pitch mask and do not dope iron. The present invention and Patent Documents 2 and 3 have a triple difference.

  Patent Document 8 is the first facet growth method, but does not use a mask with a large pitch. The growth temperature is 1050 ° C. The 5/3 group ratio b = 40. Do not iron dope. The present invention and Patent Document 8 are different in three points.

  Patent Documents 9 and 10 use a mask with a wide pitch. When the growth temperature is 1030 ° C. and 1050 ° C., the 5/3 group ratio b = 12, 12.5, and 15 times. The temperature is 1010 ° C. when the 5/3 group ratio b = 8. This is also not iron-doped. The type II of the present invention differs from Patent Documents 9 and 10 in two points. Since the surface of the type I of the present invention is almost flat, it differs from Patent Documents 9 and 10 in three respects.

  Patent Document 11 is the only document on which iron is doped. The temperature is 1000 ° C. and the 5/3 group ratio b is 50 times by MOCVD, and the temperature is 1000 ° C. and the 5/3 group ratio b is 50 times by HVPE. Do not use a mask. The present invention differs from the patent literature in three respects: growth temperature, 5/3 group ratio b, and mask presence / absence.

Since iron is doped, this cancels the intrinsic donor, and a semi-insulating nitride semiconductor substrate having a specific resistance of 10 ⁷ Ωcm or more can be obtained.

  Since a mask having a large repetitive pitch is formed on the base substrate and crystal is grown thereon, structures having different structures such as a crystal defect gathering region H, a low defect single crystal region Z, and a C-plane growth region Y can be formed. Since it relieves internal stress, a crystal with less warpage can be obtained.

  Since a mask having a large repetitive pitch is formed on the base substrate and crystal is grown thereon, structures having different structures such as a crystal defect gathering region H, a low defect single crystal region Z, and a C-plane growth region Y can be formed. Since it relieves internal stress, a substrate with less cracking can be obtained.

  Since the growth temperature is set to a high temperature of 1040 ° C. to 1150 ° C. and the 5/3 group ratio b is set to a low value of 1 to 10, a crystal with a fairly flat surface can be grown even on a base substrate on which a mask having a large repetition pitch is formed. , Thereby significantly preventing oxygen contamination.

  Since mixing of oxygen can be prevented, there is little disorder of the crystal structure, and warping and cracks are reduced.

  In Patent Document 11, iron-doped GaN is grown on a sapphire substrate by setting the substrate temperature to 1000 ° C. and increasing the 5/3 group ratio b to 50 times. As in Patent Document 11, when iron-doped GaN is vapor-phase grown directly on the base substrate, foreign iron enters and distorts the lattice structure. If the impurity concentration (iron concentration) is high, a large stress is generated and the stress cannot be relaxed, the internal strain increases, and cracks and warpage increase. If the internal stress is not relaxed, it is impossible to dope Fe at a high concentration while suppressing warping and cracking.

  In the facet growth method proposed in Patent Documents 8, 9, and 10, dislocations at peripheral portions (Z, Y) are provided by providing a mask with a wide exposed portion on a base substrate and concentrating crystal defects on the mask. Has the effect of reducing They were intended to reduce dislocations.

  In the case of a semi-insulating substrate, it is desirable that the dislocation density is low in order to withstand a large current and a high voltage.

  Further, in the facet growth methods of Patent Documents 8, 9, and 10, portions H, Z, and Y having different structures are generated in the crystal, which relieves stress. Therefore, it has been found that there is an effect of reducing warpage and suppressing the occurrence of cracks.

  Therefore, the present invention also uses the facet growth technique when making iron-doped GaN crystals. Some facet growth methods do not have a mask as in Patent Document 8, but others can specify in advance positions where H, Z, and Y portions can be formed by attaching a mask to a base substrate as in Patent Documents 9 and 10. is there.

  The structure in which the crystal defect assembly region H where defects are concentrated, the low-defect single crystal region Z with few defects, and the C-plane growth region Y alternate can relieve internal stress. Even if there is distortion due to impurity doping, the stress can be reduced.

  Therefore, the technique of facet growth with a mask is useful for the production of iron-doped GaN crystals into which impurities are introduced at a high concentration.

  Since the crystal growth is delayed in the mask covering portion and the growth is preceded in the exposed portion, facets can be formed, and the dislocation density decreases. However, it has been found that when facets are present, oxygen is further doped into the crystal through the facets as disclosed in Patent Document 7.

  Oxygen generates n-type carriers as described in Patent Document 6, so the effect of iron doping is reduced. If oxygen is taken in, it must be doped with a large amount of iron atoms to compensate for it. As a result, oxygen and iron are contained in the crystal at a high concentration.

  Neither oxygen nor iron is an essential component of GaN. When heavily doped, the crystal lattice structure is disturbed. Addition of high concentrations of oxygen and iron lowers the regularity of the crystal. It increases dislocation density and increases internal stress to increase warpage. The incidence of cracks also increases. Iron doping is inevitable to make it semi-insulating. However, oxygen is not necessary. Therefore, I want to keep the oxygen concentration as low as possible. For example, it is necessary to purify the source gas as much as possible to remove oxygen and moisture. However, it is still difficult to remove moisture completely. Some oxygen and moisture remain in the source gas.

  Oxygen does not easily enter from the C-plane as in Patent Document 7, and easily enters through facets. In other words, to reduce oxygen contamination, it seems promising to grow on the C-plane without making facets.

  Prior to Patent Documents 8, 9, and 10, C-plane growth was performed. Therefore, it can be considered that the conventional C-plane growth up to that of Patent Documents 1 to 5 is restored. However, this is the same as Patent Document 11. Unsatisfied with cracks and warping.

  The facet growth methods of Patent Documents 8, 9, and 10 have the effect of reducing not only dislocations but also reducing internal stress and reducing warpage. Instead of the dislocation reduction effect, the internal stress reduction effect is required. Therefore, the present inventor uses a mask in which the exposed portion is wider than the covered portion as in Patent Documents 9 and 10 and the pitch of the covered portion and the exposed portion is larger, and the temperature and the 5/3 group ratio b are within appropriate ranges. By controlling and suppressing facets, the inventors came up with the idea of crystal growth with less warpage and less cracking.

  For example, what should be done to grow without forming facets on a substrate provided with parallel masks of 50 μm width at intervals of 500 μm? For this purpose, it has been found that it is better to raise the growth temperature and supply more Group 3 raw materials (such as Ga).

  It has been found that when the 5/3 group ratio b is as low as 1 to 10 at a high temperature of 1080 ° C. or higher, the C plane is maintained even on a mask having a large pitch. It seems that when the 5/3 group ratio b is set to 1 to 5 at 1090 ° C. or higher, the C plane is maintained more reliably. As shown in FIG. When the substrate temperature is 1110 ° C., the 5/3 group ratio b is 1 to 10 and crystal growth occurs without forming facets. Then oxygen does not enter much. Oxygen cancels the action of iron doping, but if oxygen does not enter, the effect of iron doping appears strongly. Therefore, the nitride semiconductor crystal becomes semi-insulating. Since the growth is performed on the mask, a heterogeneous portion such as H, Z, and Y is generated. It reduces internal stress and warps and reduces cracks.

  What is necessary is just to dope the iron of the quantity which cancels even if oxygen enters. Even if a lot of impurities enter, the internal stress should be small. As already described, if there is a structure in which different parts such as H, Z, and Y are mixed, warpage and cracks can be reduced. Even if the temperature is lowered a little, the stress can be reduced if there is a mask structure. The substrate temperature is lowered to a lower temperature of about 1040 ° C. to grow a nitride semiconductor crystal on the mask structure. Then, it becomes facet growth instead of C-plane growth. As shown in FIG. Although it grows while making the facet F, it seems that oxygen penetration can be prevented to some extent if the 5/3 group ratio b is low. Furthermore, at the initial stage of growth, the temperature 5/3 group ratio b is controlled to an appropriate range so as to cause facet growth, the dislocation and internal stress are reduced, and then the temperature 5/3 group ratio is appropriately adjusted so that C plane growth is performed. A high resistance GaN substrate can be produced with a small amount of Fe doping by controlling the amount of oxygen within the above range.

  For distinction, a crystal whose surface is flat after growth as shown in FIG. A surface having a Yamatani shape as shown in FIG. 20 is called a type II.

  When the 5/3 group ratio b is as low as 1 to 10 and the temperature is 1040 ° C. to 1070 ° C., type II crystals (FIG. 20) can be formed. The crystal defect gathering region H is low, followed by faceting, and a low defect single crystal region Z can be formed therebelow. This is a cross-sectional view of an extreme case using a stripe mask and no C-plane. Even in the case of a stripe mask, there may be a C plane in the middle and a C plane growth region Y may exist. In the case of a dot mask, there is always a C plane, and a C plane growth region Y exists.

  When the 5/3 group ratio b is as low as 1 to 10 and the temperature is as high as 1090 ° C. to 1150 ° C., an I-type crystal (FIG. 21) can be formed. The surface is flat, and there are crystal defect gathering regions H immediately above the mask, which are exposed on the surface. The other part is a mixture of the low-defect single crystal region Z and the C-plane growth region Y.

  When the temperature is intermediate between them (1070 ° C. to 1090 ° C.), it becomes a mixed type. A trapezoidal crystal as shown in FIG. 24 is formed. A crystal defect gathering region H is formed on the mask. A low-defect single crystal region Z and a C-plane growth region Y are formed on the exposed portion.

  The crystal defect gathering region H generated on the mask has been considerably understood by previous studies. The crystal defect gathering region H may be simply referred to as a core. The crystal defect gathering region H is a part where dislocations are collected.

  There are three different cases of the crystal defect gathering region H.

  One is polycrystalline. There are many crystal grains with different orientations.

  In the other case, it is a single crystal whose orientation is different from that of other portions (Z, Y). The other part is a single crystal with the c-axis facing upward. Sometimes referred to as a single crystal with the c-axis inclined. Such a crystal defect gathering region H is called an inclined layer.

  The remaining one is a single crystal with the c-axis facing downward. That is, it is a single crystal in which the direction of the crystal axis is completely reversed from that of other portions (Z, Y). This is called an inversion layer. The inversion layer has the greatest power to confine dislocations. Next, the inclined layer, which is a single crystal with the c-axis inclined, has the ability to confine dislocations. Polycrystals have the weakest ability to capture dislocations.

  In any case of the dot-type stripe type, the mask provided on the base substrate is much larger in pitch than the ELO (1-2 μm diameter, 3-5 μm pitch; narrow exposed portion), and the exposed portion is wide. Therefore, it can have a structure composed of different parts such as Z, Y, and H.

  In the case of a stripe mask, the mask has a covering portion width s of 10 μm to 100 μm. The interval w between adjacent coating portions is 250 μm to 2000 μm. This is shown in FIG.

  In the case of a dot mask, the covering portion diameter s is 10 μm to 100 μm. The space | interval w of a coating part shall be 250 micrometers-2000 micrometers. This is shown in FIG. When the mask part diameter is less than 10 μm, the formation and maintenance of the crystal defect gathering region H is not successful. Even if the crystal defect gathering region H is formed, it disappears in the middle. Although the HZY structure can be formed even if the distance exceeds 2000 μm, dislocations cannot be completely captured by the crystal defect gathering region H unless the crystal is very thick.

  When the size of the mask is small as in the ELO method, the surface becomes flat (C plane) as the crystal grows, and the influence of the mask disappears immediately. However, if the size of the mask is large, the surface will not be flat even if the growth proceeds. The facet growth method (Patent Documents 9 and 10) maintains facets until the end and reduces dislocation.

  Further problems are warping and cracks. When iron-doped GaN is grown on the C-plane on a base substrate without a mask as in Patent Document 11, the substrate is cracked or strongly warped when it is used as a free-standing substrate.

  The present invention reduces internal stress by intermingling heterogeneous structures such as Z, H, and Y inside. For this purpose, a structure such as Z, H, or Y is formed using a mask having a wide pitch p (both the interval w and width s; p = s + w). However, if the facet dominates, oxygen will enter, so the crystal is made by raising the temperature and lowering the 5/3 group ratio b so that the surface is as flat as possible. Type I is more desirable.

  However, the type II is also semi-insulating, and since the warp and cracks are in a satisfactory range, the type II can also be used and is included in the scope of the present invention.

  A mask with a wide diameter (width) and interval as described above is formed on the base substrate, the substrate temperature is increased to 1040 ° C. or higher, and the 5/3 group ratio b is 1 to 10 in the HVPE method. While supplying the Group 3 raw material and the iron compound gas raw material, a nitride semiconductor crystal is synthesized on the base substrate, and the base substrate is removed. The essence of the present invention is to produce a self-supporting iron-doped nitride semiconductor crystal having a relatively small amount of oxygen, little warpage, and a low crack generation rate.

A dot mask or a stripe mask was formed using GaAs on the (111) Ga surface as a base substrate. The mask is SiO ₂ and the thickness is 60 nm to 200 nm. The mask dimensions (s, w, p) will be described later. A GaN film was grown thereon by the HVPE method. First, a buffer layer was formed, and then a thick epitaxial growth layer was formed. The conditions of the buffer layer are as follows.

Conditions for buffer layer growth
Substrate temperature 500 ° C to 550 ° C
GaCl partial pressure P _GaCl = 80 Pa (0.0008 atm)
NH ₃ partial pressure P _NHE3 = 16 kPa (0.16 atm)
Buffer layer thickness 50nm

  The 5/3 group ratio b during the growth of the buffer layer is b = 200. In the present invention, importance is attached to the growth temperature and the 5/3 group ratio b, which is a value at the time of epitaxial growth (thick film growth), and the 5/3 group ratio b at the time of forming the buffer layer is not a problem.

  In the substrate, “crack occurred” means that when a surface linear crack with a length of 2.0 mm or more occurs or when three or more surface linear cracks with a length of 0.5 mm to 2.0 mm occur. Or, it means that 21 or more surface linear cracks of 0.3 mm to 0.5 mm occurred.

  In the substrate, “crack does not occur” means that surface linear cracks of 2.0 mm or more are 0, linear cracks of 0.5 mm to 2.0 mm are 2 or less, and 0.3 mm to 0 It means that there are 20 or less 5 mm cracks.

  The crack generation rate (%) is a value obtained by dividing the number of grown substrates by the number of the total number of substrates and multiplying by 100. The donor density D refers to the concentration of n-type impurities. Here, since Si is not doped, the donor is oxygen (O). In other words, the donor density D is the oxygen concentration that creates a donor level. Both oxygen concentration and iron concentration were measured by SIMS.

  The warpage U of the substrate is expressed by a radius of curvature R (m).

  Many experiments were repeated.

  Here, 45 samples are described. Number the samples 1 to 45. Reference numerals 1-36, 44, and 45 are examples of the present invention. Samples 37 to 43 are comparative examples. Of the examples of Samples 1-36, 44, 45, Samples 1-21, 44 are I-type (flat surface). Samples 22 to 36 and 45 are type II (Yamagata).

  In the comparative example, the mask is not attached to the base substrate, and the crystal is vapor-phase grown directly on the flat base substrate. Comparative Examples 37 to 43 were specifically tested to confirm the influence of the mask and are not conventional techniques. The temperature 5/3 group ratio b may be within the limits of the present invention.

Table 1 shows the sample number, core interval (μm), core width (μm), growth temperature (° C.), PGa (GaCl partial pressure; kPa), PN (ammonia partial pressure; kPa), substrate dimensions (mm, inches ( ″), Thickness (μm), core type, crystal plane type, Fe density (cm ⁻³ ), donor density (oxygen amount; cm ⁻³ ), specific resistance (Ωcm), crack generation rate (%), warpage ( Curvature radius of curvature; m).

[Example A: Example of semi-insulating substrate]
[Sample 1 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on an 18 mm square square GaAs substrate. A feature of Sample 1 is that an 18 mm square rectangular wafer was used as the base substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more.

The GaAs substrate was processed and removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Fewer iron uptake. The specific resistance was 1 × 10 ⁷ Ωcm. The reason why the insulation is slightly low is because the iron density is low. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 4%. The crack generation rate is extremely low. The smallest of all samples. Warpage is U = 5.6 m. Warpage is small enough.

[Sample 2 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more.

The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Fewer iron uptake. The specific resistance was 1 × 10 ⁷ Ωcm. The reason why the insulation is slightly low is because the iron density is low. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 12%. The crack generation rate is extremely low. The warpage is U = 5.2 m. Warpage is small enough.

[Sample 3 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 3 inch (75 mm diameter) GaAs substrate. This is characterized by the large size of the substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more.

The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Fewer iron uptake. The specific resistance was 1 × 10 ⁷ Ωcm. The reason why the insulation is slightly low is because the iron density is low. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 18%. The crack generation rate is extremely low. Warpage is U = 6.0 m. Warpage is small enough.

[Sample 4 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more.

The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁶ cm ⁻³ . Fewer iron uptake. The specific resistance was 1 × 10 ⁶ Ωcm. The reason why the insulation is slightly low is because the iron density is low. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 12%. The crack generation rate is extremely low. Warpage is U = 5.8 m. Warpage is small enough.

[Sample 5 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 10 kPa (0.1 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 1. This sample is characterized in that the 5/3 group ratio b is set to 1. It was not frightening that the 5/3 group ratio b was so low in the growth of GaN. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁶ cm ⁻³ . Fewer iron uptake. The specific resistance was 1 × 10 ⁶ Ωcm. The reason why the insulation is slightly low is because the iron density is low. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 12%. The crack generation rate is extremely low. Warpage is U = 5.9 m. Warpage is small enough.

[Sample 6 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 3.3 kPa (0.033 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 3. This sample is characterized in that the 5/3 group ratio b is set to 3.

The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁶ cm ⁻³ . Fewer iron uptake. The specific resistance was 1 × 10 ⁶ Ωcm. The reason why the insulation is slightly low is because the iron density is low. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 15%. The crack generation rate is extremely low. Warpage is U = 5.8 m. Warpage is small enough.

[Sample 7 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁹ cm ⁻³ . A lot of iron is taken in. The specific resistance was 1 × 10 ¹¹ Ωcm. Extremely high insulation. The insulation is high because there is less oxygen (donor) and the iron concentration is high. It can be used as a semi-insulating substrate. The crack occurrence rate K was 26%. The crack occurrence rate is slightly low. Warpage is U = 5.6 m. Warpage is small enough. This is characterized by high insulation.

[Sample 8 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 5 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ¹² Ωcm. It is highly insulating. The insulation is high because there is less oxygen (donor) and the iron concentration is high. It can be used as a semi-insulating substrate. The crack occurrence rate K was 20%. The crack occurrence rate is slightly low. Warpage is U = 5.9 m. Warpage is small enough. This is characterized by a particularly high insulating property.

[Sample 9 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more.

The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is polycrystalline P. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 16%. The crack generation rate is extremely low. Warpage is U = 5.7 m. Warpage is small enough. This feature is that the crystal on the mask is not the inversion layer J but the polycrystalline P. Cracks, warpage, specific resistance, etc. are not much different from the case where the crystal on the mask is the inversion layer J.

[Sample 10 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the graded layer A. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 17%. The crack generation rate is extremely low. Warpage is U = 5.9 m. Warpage is small enough. This feature is that the crystal on the mask is not the inversion layer J but the inclined layer A. Cracks, warpage, specific resistance, etc. are not much different from the case where the crystal on the mask is the inversion layer J.

[Sample 11 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 10 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. This is characterized in that the stripe mask width s is narrowed to 10 μm (0.01 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 17%. The crack generation rate is extremely low. The warpage is U = 5.2 m. Warpage is small enough. If the mask width s is small, the warp may be larger or smaller, but even if s = 10 μm, the warp is not so large. The warpage is similar whether s = 10 μm or s = 50 μm.

[Sample 12 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 25 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. This is characterized in that the stripe mask width s is narrowed to 25 μm (0.025 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5.

The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 19%. The crack generation rate is extremely low. The warpage is U = 5.2 m. Warpage is small enough. If the mask width s is small, the warp may be larger or smaller, but even if s = 25 μm, the warp is not so large. The warpage is similar whether s = 25 μm or s = 50 μm.

[Sample 13 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 100 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. This is characterized by extending the stripe mask width s to 100 μm (0.1 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type.

The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 19%. The crack generation rate is extremely low. Warpage is U = 5.1 m. Warpage is small enough. When the mask width s is large, the warp may be larger or smaller, but even when s = 100 μm, the warp is not so large. The warpage is similar whether s = 100 μm or s = 50 μm.

[Sample 14 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 250 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. This is characterized in that the stripe interval w is narrowed to 250 μm (0.25 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 18%. The crack generation rate is extremely low. Warpage is U = 6.0 m. Warpage is small enough. If the core interval w is narrow, warpage is smaller and cracks may be reduced, but warpage and cracks do not change much even when w = 500 μm or w = 250 μm.

[Sample 15 (Example; Type I)]
A parallel stripe mask having a stripe core spacing w of w = 750 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. This is characterized in that the stripe interval w is expanded to 750 μm (0.75 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type.

The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 18%. The crack generation rate is extremely low. Warpage is U = 5.9 m. Warpage is small enough. If the core interval w is wide, the warping may be large, but even if w = 750 μm, the warping is not yet large.

[Sample 16 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 1000 μm and a mask width of s = 50 μm was formed on a 2-inch (50 mm diameter) GaAs substrate. This is characterized in that the stripe interval w is expanded to 1000 μm (1 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 17%. The crack generation rate is extremely low. Warpage is U = 5.7 m. Warpage is small enough. If the core interval w is large, the warp may be large, but even if w = 1000 μm, the warp is not yet large.

[Sample 17 (Example; Type I)]
A parallel stripe mask having a stripe core spacing w of w = 1500 μm and a mask width of s = 50 μm was formed on a 2-inch (50 mm diameter) GaAs substrate. This is characterized in that the stripe interval w is increased to 1500 μm (1.5 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 19%. The crack generation rate is extremely low. Warpage is U = 3.9 m. Warpage is slightly large. The warp U is large because the core interval w is wide (w = 1500 μm). When the allowable maximum warpage Uc is 2 m to 3.5 m, this sample substrate can also be used. When the allowable maximum warpage Uc is 4 m to 5 m, this sample is rejected. The maximum warp value Uc allowed varies depending on the purpose.

[Sample 18 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 2000 μm and a mask width of s = 50 μm was formed on a 2-inch (50 mm diameter) GaAs substrate. This is characterized in that the stripe interval w is expanded to 2000 μm (2 mm). After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J.

The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 17%. The crack generation rate is extremely low. Warpage is U = 3.3 m. Warpage is slightly large. The warp U is large because the core interval w is wide (w = 2000 μm). When the allowable maximum warpage Uc is 2 m to 3 m, the substrate of this sample can also be used. When the allowable maximum warpage Uc is 3.5 m to 5 m, this sample is rejected. The maximum warp value Uc allowed varies depending on the purpose.

[Sample 19 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . A fairly high donor density value. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁵ Ωcm. Insulation is very low. Nevertheless, it can be used as a semi-insulating substrate. The crack occurrence rate K was 24%. This is a semi-insulating substrate that can be used although cracking is somewhat frequent. Warpage is U = 5.5 m. Warpage is small.

[Sample 20 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1110 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . A fairly high donor density value. The iron density (Fe) is F = 1 × 10 ¹⁹ cm ⁻³ . A lot of iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not very high. Nevertheless, it can be used as a semi-insulating substrate. The crack occurrence rate K was 16%. Good semi-insulating substrate with little cracking. The warpage is U = 5.2 m. Warpage is small.

[Sample 21 (Example; Type I)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. The epitaxial growth temperature is Tg = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), GaCl partial pressure P _GaCl = 4 kPa (0.04 atm), and epitaxial growth is performed until the thickness reaches 400 μm or more, then Tq = 1110 Epitaxial growth was performed at a temperature of 1000 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm). A GaN substrate was cut out from a portion grown at 1100 ° C. after removing the GaAs substrate, and a single independent substrate of GaN having a thickness of 400 μm was obtained.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . A fairly high donor density value. The iron density (Fe) is F = 5 × 10 ¹⁹ cm ⁻³ . A lot of iron is taken in. The specific resistance was 1 × 10 ⁸ Ωcm. Insulation is slightly high. It can be used as a semi-insulating substrate. The crack occurrence rate K was 27%. It is a semi-insulating substrate that can be used although there are quite many cracks. Warpage is U = 5.3 m. Warpage is small.

[Sample 22 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not very high. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 17%. Good semi-insulating substrate with little cracking. Warpage is U = 5.0 m. Warpage is small.

[Sample 23 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁶ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁶ Ωcm. Insulation is slightly low. Nevertheless, it can be used as a semi-insulating substrate. The crack occurrence rate K was 13%. Good semi-insulating substrate with little cracking. Warpage is U = 5.5 m. Warpage is small.

[Sample 24 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . It is a fairly high value. The iron density (Fe) is F = 1 × 10 ¹⁹ cm ⁻³ . A lot of iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 16%. Good semi-insulating substrate with little cracking. Warpage is U = 5.7 m. Warpage is small.

[Sample 25 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . It is a fairly high value. The iron density (Fe) is F = 5 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ⁸ Ωcm. Insulation is slightly high. It can be used as a semi-insulating substrate. The crack occurrence rate K was 29%. Although it is a considerably large value, it is a useful substrate. Warpage is U = 5.3 m. Warpage is small.

[Sample 26 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁹ cm ⁻³ . Extremely high value. The iron density (Fe) is F = 7 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ⁵ Ωcm. Insulation is very low. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 29%. Although it is a considerably large value, it is a useful substrate. Warpage is U = 6.0 m. Warpage is small.

[Sample 27 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁹ cm ⁻³ . Extremely high value. The iron density (Fe) is F = 8 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 28%. Although it is a considerably large value, it is a useful substrate. Warpage is U = 5.1 m. Warpage is small.

[Sample 28 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . It is a fairly high value. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Slightly less iron uptake. The specific resistance was 1 × 10 ⁵ Ωcm. Insulation is very low. However, it can be used as a semi-insulating substrate. The crack occurrence rate K was 23%. Although it is a considerably large value, it is a useful substrate. Warpage is U = 5.7 m. Warpage is small.

[Sample 29 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . It is a low value. The iron density (Fe) is F = 1 × 10 ¹⁹ cm ⁻³ . A lot of iron is taken in. The specific resistance was 1 × 10 ¹¹ Ωcm. Insulation is extremely high. It can be used as a semi-insulating substrate. The crack occurrence rate K was 27%. Although it is a considerably large value, it is a useful substrate. Warpage is U = 5.4 m. Warpage is small.

[Sample 30 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . It is a low value. The iron density (Fe) is F = 5 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ¹² Ωcm. Insulation is extremely high. The crack occurrence rate K was 18%. This is a fairly low value. Warpage is U = 5.7 m. Small warpage.

[Sample 31 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁹ cm ⁻³ . Very high value. The iron density (Fe) is F = 7 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ⁵ Ωcm. Insulation is very low. The crack occurrence rate K was 27%. This is a fairly high value but still a useful substrate. Warpage is U = 6.0 m. Small warpage.

[Sample 32 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁹ cm ⁻³ . Extremely high value. The iron density (Fe) is F = 8 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. The crack occurrence rate K was 29%. This is a fairly high value but still a useful substrate. Warpage is U = 5.6 m. The warpage is small.

[Sample 33 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Low donor density. The iron density (Fe) is F = 7 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 3 × 10 ¹² Ωcm. Insulation is extremely high. The crack occurrence rate K was 27%. This is a fairly high value but still a useful substrate. Warpage is U = 5.5 m. The warpage is small.

[Sample 34 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . It is a low value. A large amount of oxygen is doped because it is type II. The iron density (Fe) is F = 8 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 5 × 10 ¹² Ωcm. Insulation is extremely high. The crack occurrence rate K was 28%. This is a fairly high value but still a useful substrate. Warpage is U = 5.0 m. The warpage is small.

[Sample 35 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 2 kPa (0.02 atm) until the thickness reached 400 μm or more.

The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁹ cm ⁻³ . A large amount of oxygen is doped because it is type II. The iron density (Fe) is F = 7 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ⁵ Ωcm. Insulation is very low. The crack occurrence rate K was 29%. This is a fairly high value but still a useful substrate. Warpage is U = 5.0 m. The warpage is small.

[Sample 36 (Example; Type II)]
A parallel stripe mask having a stripe core interval w of w = 500 μm and a mask width of s = 50 μm was formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 1 kPa (0.01 atm) until the thickness reached 400 μm or more.

The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 10. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁹ cm ⁻³ . Extremely high value. A large amount of oxygen is doped because it is type II. The amount of iron (Fe) is F = 8 × 10 ¹⁹ cm ⁻³ . An extremely large amount of iron is taken up. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. The crack occurrence rate K was 28%. This is a fairly high value but still a useful substrate. Warpage is U = 5.0 m. The warpage is small.

[Sample 37 (comparative example; no mask)]
No mask is formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. Since there is no mask, there is no core. A uniformly flat C-plane crystal grows on the substrate. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal plane exposed on the surface is the C plane. The C surface is a flat surface. Since there is no mask, it is C-plane growth. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Since it is C-plane growth, oxygen (donor) hardly enters the crystal and the donor density is extremely low. Oxygen is hardly doped. The amount of iron (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . Considerable iron is taken in. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not high. Crack generation rate K was 77%. Very high value. The warpage is U = 1.4 m. That is, the warpage is large. This is because GaN was grown without making a mask on the underlying substrate. It is not suitable as a substrate on which a device is formed.

[Sample 38 (comparative example; no mask)]
No mask is formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. Since there is no mask, there is no core. A uniformly flat C-plane crystal grows on the substrate. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal plane exposed on the surface is the C plane. The C surface is a flat surface. Since there is no mask, it is C-plane growth. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Since it is C-plane growth, oxygen (donor) hardly enters the crystal and the donor density is extremely low. Oxygen is hardly doped. The amount of iron (Fe) is F = 1 × 10 ¹⁶ cm ⁻³ . Iron uptake is very low. The specific resistance was 1 × 10 ⁶ Ωcm. Insulation is slightly low. The crack occurrence rate K was 75%. Extremely high value. The warpage is U = 1.6 m. That is, the warpage is large. This is because GaN was grown without making a mask on the underlying substrate. It is not suitable as a substrate on which a device is formed.

[Sample 39 (comparative example; no mask)]
No mask is formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. The epitaxial growth temperature was epitaxial growth until Tq = 1030 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) thickness was 400 μm or more. Since there is no mask, there is no core. A uniformly flat C-plane crystal grows on the substrate. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal plane exposed on the surface is the C plane. The C surface is a flat surface. Since there is no mask, it is C-plane growth. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Since it is C-plane growth, oxygen (donor) hardly enters the crystal and the donor density is extremely low. Oxygen is hardly doped. The amount of iron (Fe) is F = 1 × 10 ¹⁹ cm ⁻³ . Iron is incorporated in a fairly high concentration. The specific resistance was 1 × 10 ¹¹ Ωcm. Insulation is high. The crack occurrence rate K was 88%. Extremely high value. Warpage is U = 1.9 m. That is, the warpage is large. It is not suitable as a substrate on which a device is formed.

[Sample 40 (comparative example; no mask)]
No mask is formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1030 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. Since there is no mask, there is no core. A uniformly flat C-plane crystal grows on the substrate. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal plane exposed on the surface is the C plane. The C surface is a flat surface. Since there is no mask, it is C-plane growth. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Since it is C-plane growth, oxygen (donor) hardly enters the crystal and the donor density is extremely low. Oxygen is hardly doped. The amount of iron (Fe) is F = 5 × 10 ¹⁹ cm ⁻³ . High concentration of iron. Specific resistance is 1 × 10 ¹²
cm. Insulation is high. The crack occurrence rate K was 97%. Extremely high value. The warpage is U = 1.8 m. That is, the warpage is large. It is not suitable as a substrate on which a device is formed.

[Sample 41 (comparative example; no mask)]
No mask is formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. The epitaxial growth temperature was Tq = 1010 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. Since there is no mask, there is no core. A uniformly flat C-plane crystal grows on the substrate. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal plane exposed on the surface is the C plane. The C surface is a flat surface. Since there is no mask, it is C-plane growth. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . Although it is C-plane growth, it has a fairly high donor density. The amount of iron (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . A lot of iron is taken in. Specific resistance is 1 × 10 ⁵
cm. Insulation is very low. The crack occurrence rate K was 68%. High value. The warpage is U = 1.4 m. That is, the warpage is large. It is not suitable as a substrate on which a device is formed.

[Sample 42 (comparative example; no mask)]
No mask is formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. The epitaxial growth temperature was Tq = 1010 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. Since there is no mask, there is no core. A uniformly flat C-plane crystal grows on the substrate. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal plane exposed on the surface is the C plane. The C surface is a flat surface. Since there is no mask, it is C-plane growth. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . Although it is C-plane growth, it has a fairly high donor density. The amount of iron (Fe) is F = 1 × 10 ¹⁹ cm ⁻³ . High concentration of iron. The specific resistance was 1 × 10 ⁷ cm. Insulation is not high. The crack occurrence rate K was 90%. Extremely high value. The warpage is U = 1.4 m. That is, the warpage is large. It is not suitable as a substrate on which a device is formed.

[Sample 43 (comparative example; no mask)]
No mask is formed on a 2 inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. Since there is no mask, there is no core. A uniformly flat C-plane crystal grows on the substrate. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal plane exposed on the surface is the C plane. The C surface is a flat surface. Since there is no mask, it is C-plane growth. The donor density is D = 1 × 10 ¹⁷ cm ⁻³ . Although it is C-plane growth, it has a fairly high donor density. The amount of iron (Fe) is F = 5 × 10 ¹⁹ cm ⁻³ . High concentration of iron. The specific resistance was 1 × 10 ⁸ cm. Insulation is slightly high. The crack occurrence rate K was 95%. Extremely high value. The warpage is U = 1.6 m. That is, the warpage is large. This is because no mask was formed. It is not suitable as a substrate on which a device is formed.

[Sample 44 (Example; Type I, dot type)]
A dot mask having a dot core interval w of w = 500 μm and a mask diameter of s = 50 μm was formed on a 2-inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1100 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more.

The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm. The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type I. Since the growth temperature Tq was high, it became I type. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . There is not much iron uptake. The specific resistance was 1 × 10 ⁷ Ωcm. The reason why the insulation is slightly low is because the iron density is low. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 20%. The crack generation rate is extremely low. The warpage is U = 3.2 m.

[Sample 45 (Example; type II, dot type)]
A dot mask having a dot core interval w of w = 500 μm and a mask diameter of s = 50 μm was formed on a 2-inch (50 mm diameter) GaAs substrate. After forming the buffer layer, epitaxial growth was performed. Epitaxial growth was performed at an epitaxial growth temperature of Tq = 1050 ° C., NH ₃ partial pressure P _NH3 = 10 kPa (0.1 atm), and GaCl partial pressure P _GaCl = 4 kPa (0.04 atm) until the thickness reached 400 μm or more. The GaAs substrate was removed to obtain a single independent substrate of GaN having a thickness of 400 μm.

The 5/3 group ratio b is b = 2.5. The crystal type of the core is the inversion layer J. The crystal face type is type II. Since the growth temperature Tq was slightly low, it became type II. The donor density is D = 1 × 10 ¹⁵ cm ⁻³ . Very low donor density values. The iron density (Fe) is F = 1 × 10 ¹⁷ cm ⁻³ . There is not much iron uptake. The specific resistance was 1 × 10 ⁷ Ωcm. Insulation is not very high. However, it can still be used as a semi-insulating substrate. The crack occurrence rate K was 18%. Good semi-insulating substrate with little cracking. Warpage is U = 4.0 m. Warpage is small.

[Example B: Example of device using semi-insulating substrate]
[Production of devices using striped semi-insulating substrate]
[Device Sample 46 (Example; Type I)]
Crystal type I type 3 inch semi-insulating substrate prepared in Sample 3 (stripe core spacing 500 μm, mask width 50 μm) on a substrate having a specific resistance of 1 × 10 ⁷ Ωcm by metal organic vapor phase epitaxy (OMVPE). An epitaxial wafer having a high electron mobility transistor structure was fabricated (FIG. 28). A GaN substrate was placed in the reactor of the OMVPE apparatus, a gas containing hydrogen, nitrogen, and ammonia was supplied into the reactor, and heat treatment was performed at a temperature of 1100 ° C. for 20 minutes. Next, the temperature of the GaN substrate was raised to 1130 ° C., ammonia and trimethylgallium (TMG) were supplied to the reactor, and a GaN epilayer having a thickness of 1.5 μm was grown on the GaN substrate. Trimethylaluminum (TMA), TMG, and ammonia were supplied to the reactor, and an AlGaN film having a thickness of 30 nm and an Al composition of 20% was grown on the GaN epilayer. An epitaxial substrate (FIG. 28) was produced by these steps.

Next, a HEMT device (FIG. 29) was produced by the following steps. A source electrode and a drain electrode were formed on the surface of the epitaxial substrate (FIG. 28) by photolithography, EB vapor deposition, and lift-off. Ti / Al / Ti / Au (20/100/20/300 nm) was used for the electrode. After lift-off, an alloying heat treatment was performed at 600 ° C. for 1 minute.

Next, a gate electrode was produced by the same process. The gate was arranged in a direction parallel to the stripe core (defect gathering region) so as not to be formed on the stripe core. Ni / Au (50/500 nm) was used as the gate electrode. The gate length was 2 μm. (This is referred to as a device sample 46.)

[Device sample 47 (comparative example)]
As a comparative sample 47, HEMT structure epi-growth was similarly performed on an Fe-doped semi-insulating random core substrate to produce a HEMT. The random core is a crystal in which the crystal defect gathering regions H are randomly distributed. When facet growth is performed without attaching a mask on the base substrate, facet pits are randomly generated and become crystal defect gathering regions H, so that the crystal defect gathering regions H (cores) are randomly distributed.

[Device Sample 48 (Comparative Example)]
Further, HEMT structure epi-growth was similarly performed on a sapphire substrate as a comparative sample 48. In the epi-growth step, the sapphire substrate is heat treated at 1170 ° C. for 10 minutes, and then a seeding layer is grown. FIG. 30). Next, HEMT fabrication was performed in the same process (FIG. 31).

The gate leakage currents of the device samples 46, 47, and 48 were compared. At a gate voltage of 5 V, a small value of 1 × 10 ⁶ A / cm ² was obtained for the sample 46, but 1 × 10 ³ A / cm ^{2 for} the sample 47 and 1 × 10 ² A / cm for the sample 48. ² and the sample 46, the gate leakage current increased greatly. The smaller the gate leakage current, the better the pinch-off of the transistor, so that a high-performance transistor can be realized.

The reason why the gate leakage current increased in the device sample 47 is thought to be that a random core was present under the gate electrode and the leakage current due to dislocation increased.

The reason why the gate leakage current increased in the device sample 48 was that the dislocation density in the epi layer increased (˜1 × 10 ⁹ / cm ² ) due to the sapphire substrate, and the leakage current due to the dislocation increased. Conceivable.
As described above, according to the present invention, a high-performance HEMT and HEMT epitaxial substrate with a small gate leakage current can be realized.

[Example C: Example of device using dot type semi-insulating substrate]
[Production of devices using dot-type semi-insulating substrate]
[Device sample 49 (Example; I type, dot type)]
A crystal type I type 2 inch semi-insulating substrate (dot core spacing: 500 μm, mask diameter: 50 μm) fabricated on Sample 44 is formed on a substrate having a specific resistance of 1 × 10 ⁷ Ωcm by metal organic vapor phase epitaxy (OMVPE). An epitaxial wafer having a high electron mobility transistor structure was fabricated (FIG. 28). A GaN substrate was placed in the reactor of the OMVPE apparatus, a gas containing hydrogen, nitrogen, and ammonia was supplied into the reactor, and heat treatment was performed at a temperature of 1100 ° C. for 20 minutes. Next, the temperature of the GaN substrate was raised to 1130 ° C., ammonia and trimethylgallium (TMG) were supplied to the reactor, and a GaN epilayer having a thickness of 1.5 μm was grown on the GaN substrate. Trimethylaluminum (TMA), TMG, and ammonia were supplied to the reactor, and an AlGaN film having a thickness of 30 nm and an Al composition of 20% was grown on the GaN epilayer. An epitaxial substrate (FIG. 28) was produced by these steps.

Next, a HEMT device (FIG. 29) was produced by the following steps. A source electrode and a drain electrode were formed on the surface of the epitaxial substrate (FIG. 28) by photolithography, EB vapor deposition, and lift-off. Ti / Al / Ti / Au (20/100/20/300 nm) was used for the electrode. After lift-off, an alloying heat treatment was performed at 600 ° C. for 1 minute.

Next, a gate electrode was produced by the same process. The gate electrode was prepared so as not to be formed on the dot core region (defect assembly region). Ni / Au (50/500 nm) was used as the gate electrode. The gate length was 2 μm. (This is referred to as a device sample 49.)

[Device sample 50 (comparative example)]
As a comparative sample 50, HEMT structure epi-growth was similarly performed on an Fe-doped semi-insulating random core substrate to produce a HEMT.

[Device Sample 51 (Comparative Example)]
Further, HEMT structure epi-growth was similarly performed on a sapphire substrate as a comparative sample 51. In the epi-growth step, the sapphire substrate is heat treated at 1170 ° C. for 10 minutes, and then a seeding layer is grown. FIG. 30). Next, HEMT fabrication was performed in the same process (FIG. 31).

The gate leakage currents of the device samples 49, 50, and 51 were compared. At a gate voltage of 5 V, a small value of 1 × 10 ⁶ A / cm ² was obtained for sample 49, but 1 × 10 ³ A / cm ² for sample 50 and 1 × 10 ² A / cm for sample 51. Compared with ² and sample 49, the gate leakage current increased greatly. The smaller the gate leakage current, the better the pinch-off of the transistor, so that a high-performance transistor can be realized.

The reason why the gate leakage current increased in the device sample 50 is thought to be that a random core exists under the gate electrode and the leakage current due to dislocation increased.

The reason why the gate leakage current increased in the device sample 51 was that the dislocation density in the epi layer increased (˜1 × 10 ⁹ / cm ² ) because the substrate was sapphire, and the leakage current due to the dislocation increased. Conceivable.
As described above, according to the present invention, a high-performance HEMT and HEMT epitaxial substrate with a small gate leakage current can be realized.

  For the above Examples 1 to 36, 44, and 45, the values of the temperature and the 5/3 group ratio b are shown by white circles (II type) and white triangles (I type) in FIG. All are in the range surrounded by a broken line (1040 ° C. to 1150 ° C., 5/3 group ratio b = 1 to 10). In Comparative Examples 37 to 43, regarding the temperature and the 5/3 group ratio b, there are some that are included in the inside of the broken line frame and some that are not included. Even within the broken line frame, these comparative examples are not suitable in terms of cracks and warpage. This is because no mask is attached. The comparative example is for examining the effect of the mask.

  FIG. 23 shows the rate of warpage of samples 1 to 45, with the curvature radius (m) of warpage being the horizontal axis and the crack generation rate (%) being the vertical axis, and warping by the points. The subscript number represents the sample number. White circles indicate type I samples 1-21, 44. White triangles represent Type II samples 22-36, 45. White squares correspond to samples 37 to 43 of the comparative example.

  The samples 37 to 43 of the comparative example have strong warpage (the radius of curvature is 1 m to 2 m) and the crack generation rate is 68 to 97%, which is inappropriate as a substrate for manufacturing a semiconductor device. This is because the base substrate has no mask.

  Comparing type I and type II, the warp (curvature radius) is between 5 m and 6 m and does not change much. The curvature radius of warpage is 3 m or more for both I and II types. It is distributed between 3m and 7m. The crack occurrence rate is 30% or less. The crack occurrence rate is between 4% and 27% for type I, and most is distributed between 10% and 20%. Type II has a crack generation rate between 13% and 29%, and most is between 25% and 29%. From the viewpoint of cracks, the I type is superior to the II type. Both type I and type II can be used as semi-insulating substrates.

FIG. 27 is a graph showing the distribution of donor density (cm ⁻³ ) and iron (Fe) density (cm ⁻³ ) of Samples 1 to 45. The horizontal axis represents the donor (oxygen) density, and the vertical axis represents the iron density. White circles are type I, white triangles are type II, and white squares are comparative examples. The subscript represents the sample number. It can be seen that type II (white triangle) has a high donor density. Some of them are type I and have a high donor density (samples 19, 20, and 21). Most of type I have a low donor density.

  In type II, the amount of iron doped and the amount of donor increase roughly proportionally, but in type I, the amount of iron can be increased even if the amount of donor is small. In this respect, the I type is more excellent.

Furthermore, the dislocation density of the samples I-II type 1-36 and the samples of Comparative Examples 37-43 were measured by etching at 200 ° C. with an etching solution of phosphoric acid and sulfuric acid. The measurement was performed by counting the number of etch pits in a region of 100 × 100 μm using a 100 × objective of a differential interference optical microscope. As a result, the dislocation density (etch pit density) of the samples of Comparative Examples 37 to 43 is all 2 × 10 ⁷ to 10 ⁸ / cm ² , while all of the samples 1 to 36 are 5 × 10 ^6. / Cm ² or less, especially those whose curvature radius of crystal exceeds 4 m is 2 × 10 ⁶ / cm ² or less, those that exceed 5 m are 10 ⁵ / cm ² or less, and the type of crystal plane is II The thing was about half compared with I. However, although the sample 21 is facet-grown at the initial stage of growth despite the crystal plane type being I, the sample 21 is approximately half the type compared to the samples 2, 11, 12, and 20 having substantially the same radius of curvature. The dislocation density was the same as that of Sample 25 having the same curvature radius in II.
Further, even if a sapphire substrate or a SiC substrate is used instead of the GaAs substrate used for the preparation of samples 1 to 36, the crystal plane, Fe density, donor density, specific resistance, crack generation rate, warpage equivalent to those of samples 1 to 36 are used. A substrate having a radius of curvature of
In addition, as a result of growing the GaN substrate of Samples 1 to 36 under the same conditions as Samples 1 to 36, the same crystal plane, Fe density, donor density, specific resistance, crack generation rate as Samples 1 to 36 were obtained. A substrate having a curvature radius of warpage was obtained.

The top view of the mask in which many small windows (exposed part) exist in a narrow repeated pitch in the wide coating | coated part formed on the base substrate.

Process drawing for demonstrating the process of vapor-phase-growing a gallium nitride on the mask on a base substrate.

The partial perspective view of the crystal | crystallization by the random facet growth method in which many facet pits from which a dimension differs on the crystal | crystallization surface generate | occur | produce at random.

In facet growth that maintains facet pits until the end of growth, the growth direction and the dislocation direction are parallel, so the dislocations extend in the facet normal direction and reach the facet boundary, descend along the boundary and descend to the bottom of the pit. The pit perspective view for demonstrating gathering.

In facet growth that maintains facet pits until the end of growth, the growth direction and the dislocation direction are parallel, so the dislocations extend in the facet normal direction and reach the facet boundary, descend along the boundary and descend to the bottom of the pit. The pit top view for demonstrating gathering.

FIG. 2 is a plan view of a part of a dot-type mask formed on a base substrate for maintaining facet pits until the end of growth, in which a large number of dot-shaped covering portions are regularly and vertically arranged at wide intervals.

The perspective view of the surface of the GaN crystal by the dot type facet growth method which produced the facet pit which has a bottom on the coating | coated part M by carrying out vapor phase growth of the GaN crystal on the base substrate which provided the dot type mask.

The top view of the GaN crystal by the dot type facet growth method which produced the facet pit which has a bottom on the coating | coated part M by carrying out the vapor phase growth of the GaN crystal on the base substrate which provided the dot type mask.

A vapor phase growth of a GaN crystal on a base substrate provided with a dot-type mask creates a facet pit with a bottom on the covering portion M, the facet pit becomes large, and a crystal defect gathering region H is generated on the mask. The longitudinal cross-sectional view for every process of the facet growth which shows the process of.

A plan view of a part of a striped mask formed on a base substrate and having a plurality of parallel line-shaped covering portions regularly and vertically with a wide interval in order to perform facet growth that maintains facet pits until the end of growth. .

A GaN crystal is vapor-phase-grown on a base substrate provided with a stripe-type mask, and a valley is present on the covering portion M, a flat top surface is present in the middle of the covering portion, and a facet inclined between the top surface and the valley exists. The top view of the GaN crystal by the stripe type facet growth method which produced many mountain valley structures.

A GaN crystal is vapor-phase-grown on a base substrate provided with a stripe-type mask, and a valley is present on the covering portion M, a flat top surface is present in the middle of the covering portion, and a facet inclined between the top surface and the valley exists. The perspective view of the GaN crystal by the stripe type facet growth method which produced many mountain valley structures.

A GaN crystal is vapor-phase-grown on a base substrate provided with a stripe mask, a valley is formed on the covering portion M, a sharp ridge line is present in the middle of the covering portion, and many facets are inclined between the sharp ridge line and the valley. The top view of the GaN crystal by the stripe type facet growth method which produced the mountain-valley structure.

A GaN crystal is vapor-phase-grown on a base substrate provided with a stripe mask, a valley is formed on the covering portion M, a sharp ridge line is present in the middle of the covering portion, and many facets are inclined between the sharp ridge line and the valley. The perspective view of the GaN crystal by the stripe-type facet growth method which created the mountain-valley structure.

When a stripe mask is formed on the base substrate and GaN is vapor-phase grown on the mask, the growth proceeds first in the exposed portion, so that a crystal having a C-face and a facet grows on the exposed portion, and is formed on the mask. FIG. 6 is a process cross-sectional view showing a process in which a low crystal defect gathering region H is formed, and a parallel mountain-valley structure is formed in which a valley is directly above the mask and a peak is in the middle of the mask.

FIG. 16 is a process cross-sectional view showing a process in which the crystal growth further progresses after FIG. 15 and the mountain becomes higher and the valley becomes larger in the stripe mask facet method.

Patent Document 7 (Patent No. 3826825) proposes that oxygen has little selectivity from the C-plane and is taken in a large amount through the facet, so that it grows in the c-axis direction by making facets. FIG. 3 is a cross-sectional view of a GaN crystal that can be doped with oxygen at a high concentration.

Patent Document 7 (Patent No. 3826825) proposes that oxygen has little selectivity from the C-plane and passes through facets and is taken in a large amount into the crystal, making crystals with surfaces other than the C-plane. FIG. 3 is a cross-sectional view of a GaN crystal in which oxygen can be doped at a high concentration by crystal growth of GaN thereon.

1 is a cross-sectional view of an HVPE furnace for producing the iron-doped nitride semiconductor crystal of the present invention.

Sectional drawing which shows the shape of the II type nitride semiconductor crystal with the mountain-valley structure produced by the method of this invention.

Sectional drawing which shows the shape of the I-type nitride semiconductor crystal with the flat surface produced by the method of this invention.

The graph which shows the growth temperature and 5/3 group ratio b as a coordinate for every Example in the vapor phase growth method of patent documents 1-11 which describe a prior art, and the vapor phase growth method of this invention. The horizontal axis is the growth temperature (° C.). The vertical axis represents the 5/3 group ratio b in logarithm.

The graph which showed the curvature radius (m) and crack generation rate (%) of the curvature of the samples 1-43 which are the Example of this invention, and a comparative example by the point in the space which uses curvature and a crack as an abscissa. The number shaken is the sample number. White circles are type I, white triangles are type II, and white squares are comparative examples. Comparative examples are not known.

Sectional drawing which shows the shape of the mixed type nitride semiconductor crystal of I and II which has a facet part in the flat surface part produced with the method of this invention.

The top view which shows the dimension of width | variety s of a stripe mask and the space | interval w in the method of this invention which forms the stripe mask which consists of several parallel coating | coated parts in a base substrate, and vapor-phase-grows a nitride semiconductor on it.

The top view which shows the dimension of the diameter s of a dot mask, and the dimension of the space | interval w in the method of this invention which forms the dot mask which consists of vertical and horizontal parallel several point-like covering part in a base substrate, and carries out vapor phase growth of the nitride semiconductor on it.

In the graph using the logarithm of the donor density (cm ⁻³ ) and the logarithm of the iron density (cm ⁻³ ) as the horizontal and vertical coordinates, the samples 1 to 43 of vapor phase growth of GaN described in the specification of the present invention are indicated by dots. What you represent. The numbers are the sample numbers. White circles are type I, white triangles are type II, and white squares are comparative examples. Comparative examples are not known.

The longitudinal cross-sectional view of the epitaxial substrate which made the GaN thin film grow on the SI-GaN (semi-insulating GaN) substrate.

The longitudinal cross-sectional view of HEMT created by attaching an electrode on the epitaxial substrate which grew the GaN thin film on the SI-GaN (semi-insulating GaN) substrate.

The longitudinal cross-sectional view of the epitaxial substrate which made the GaN thin film grow on the sapphire substrate.

The longitudinal cross-sectional view of HEMT produced by attaching an electrode on the epitaxial substrate which grew the GaN thin film on the sapphire substrate.

Explanation of symbols

U Underlying substrate
M Mask cover
E Exposed part not covered by mask
W mask window
T dislocation
G crystal
F facet
C C side
P facet pit
V Growth direction
H Crystal defect assembly region (Closed defect assembly region)
Z Low defect single crystal region (Single crystal low dislocation associated region)
Y C-plane growth region (single crystal low dislocation residual region)
K grain boundary
s Diameter or width of mask cover
w Mask cover interval
p Repeat pitch of mask coating
2 Reactor
3 Heater
4 Ga reservoir
5 Susceptors
6 Substrate
7 First source gas supply pipe
8 Second source gas supply pipe
9 Gas exhaust pipe
10 Third source gas supply pipe

Claims (6)

On the base substrate, a mask in which dot coating portions or stripe coating portions having a width or diameter s of 10 μm to 100 μm are arranged so that the interval w is 250 μm to 2000 μm is formed, and the growth temperature is from 1040 ° C. to HVPE. A nitride semiconductor crystal is grown on the base substrate by supplying a Group 3 or Group 5 source gas having a 1/3 degree b ratio of 1 to 10 at 1150 ° C. and a gas containing iron. And removing the base substrate to obtain a self-supporting semi-insulating nitride semiconductor substrate having a specific resistance of 1 × 10 ⁵ Ωcm or more and a thickness of 100 μm or more. A method for manufacturing a substrate. 2. The crystal according to claim 1, wherein the growth temperature is 1090 ° C. to 1150 ° C., the 5/3 group ratio b is 1 to 5, and the surface is substantially flat except for the covering portion. A method of manufacturing a semi-insulating nitride semiconductor substrate. A growth temperature is 1040 ° C. to 1070 ° C., a 5/3 group ratio b is 1 to 10, and a crystal having a facet plane with a covering portion as a bottom and a middle portion between adjacent covering portions as a peak is grown. The method for producing a semi-insulating nitride semiconductor substrate according to claim 1. Low defect single crystal having a diameter or width s of 10 μm to 100 μm and an interval w of 250 μm to 2000 μm and repeatedly existing between a point-like or parallel-line crystal defect gathering region H and adjacent crystal defect gathering regions H, H Including a region Z and a C-plane growth region Y existing between the low-defect single crystal regions Z and Z, having a specific resistance of 1 × 10 ⁵ Ωcm or more, a thickness of 100 μm or more, and a curvature radius of curvature of 3 m or more. A semi-insulating nitride semiconductor substrate characterized by: Low defect single crystal having a diameter or width s of 10 μm to 100 μm and an interval w of 250 μm to 2000 μm and repeatedly existing between a point-like or parallel-line crystal defect gathering region H and adjacent crystal defect gathering regions H, H A semi-insulating nitride semiconductor substrate including a region Z and a C-plane growth region Y existing between the low-defect single crystal regions Z and Z, a specific resistance of 1 × 10 ⁵ Ωcm or more, and a thickness of 100 μm or more, A nitride semiconductor epitaxial substrate comprising a nitride semiconductor epitaxial film provided on a substrate, wherein a curvature radius of warpage is 3 m or more. Low defect single crystal having a diameter or width s of 10 μm to 100 μm and an interval w of 250 μm to 2000 μm and repeatedly existing between a point-like or parallel-line crystal defect gathering region H and adjacent crystal defect gathering regions H, H A semi-insulating nitride semiconductor substrate including a region Z and a C-plane growth region Y existing between the low-defect single crystal regions Z and Z and having a specific resistance of 1 × 10 ⁵ Ωcm or more;
A nitride semiconductor epitaxial film provided on the semi-insulating nitride semiconductor substrate;
A gate electrode provided on the nitride semiconductor epitaxial film;
A source electrode provided on the nitride semiconductor epitaxial film;
A field effect transistor comprising a drain electrode provided on the nitride semiconductor epitaxial film, wherein the gate electrode is formed in a region other than the crystal defect assembly region H.

Images