KR101369967B1 - Manufacturing Method of Free Standing GaN Wafer without Bowing Property - Google Patents

Abstract

The present invention is to provide a method for producing a GaN free-standing substrate by growing a GaN thick film crystallized from the deflection, the method of manufacturing a gallium nitride free-standing substrate according to an aspect of the present invention, a predetermined ratio in a heated reactor Supplying GaCl gas and NH ₃ gas to grow GaN crystals to the substrate in the reactor to a predetermined time, and reducing the supply amount of the NH ₃ gas to a predetermined ratio relative to the initial supply after the predetermined time, In the reducing step, as the thickness of GaN crystals grown on the substrate increases, the supply amount of the NH ₃ gas is decreased to increase nitrogen vacancies in the GaN crystals.

Description

Manufacturing Method of Free Standing GaN Wafer without Bowing Property}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN free-standing substrate manufacturing method, and more particularly, to a method of manufacturing a GaN free-standing substrate by removing warpage of a grown GaN thick film by HVPE (Hydride Vapor Phase Epitaxy) method.

Nitride semiconductor materials such as AlN, GaN, InN, etc. are direct transition semiconductor materials with band gaps ranging from 0.65 eV to 6.2 eV, so these three materials form a solid-solution to emit all visible light from infrared to ultraviolet. As a light emitting device, light emitting diodes (LEDs) and laser diodes (LDs) are gaining popularity.

A method of growing a nitride semiconductor such as GaN includes HVPE (Hydride Vapor Phase Epitaxy), MOCVD (Metalorganic Vapor Phase Epitaxy), and MBE (Molecular Beam Epitaxy). The method is advantageous.

The HVPE growth apparatus may be configured as shown in FIG. 1. A computer-controlled reactor is divided into a source zone in which raw materials are supplied and a growth zone in which growth occurs. A source zone includes a boat containing Ga metal. And a NH ₃ supply tube under control of a gas supply connected to the gas cabinet, an HCl supply tube for reacting with Ga metal to generate GaCl, and a dopant supply tube for doping. You will get the gas you need.

For example, in the conventional GaN wafer manufacturing method using the HVPE method, a thick GaN film with a thickness of about 300 to 600 µm is grown on a heterogeneous substrate such as a sapphire substrate, a GaAs substrate, or a Si substrate by HVPE method, but the defect density is about It has a quality of 3 ~ 5x10 ⁶ / ㎠. The GaN free-standing substrate is completed by separating the GaN thick film from the dissimilar substrate, mirror-processing the separated GaN thick film surface, and removing the damaged layer present on the surface.

However, when GaN independent substrates are manufactured by separating GaN thick films grown on heterogeneous substrates by the HVPE method, the conventional GaN independent substrates are generally concave toward the surface as shown in FIG. 2. The reason why the GaN independent substrate is bent in this way is that crystal defects such as dislocations increase toward the bottom of the substrate. That is, due to the difference between the lattice constant of the dissimilar substrate and the lattice constant of GaN, a large number of crystal defects such as dislocations are generated at the initial stage of crystal growth, and as the thickness of GaN crystals increases, crystal defects such as dislocations decrease, thereby improving the crystal quality. The separated GaN free-standing substrate is characterized by the largest number of crystal defects such as dislocations in the bottom portion attached to the dissimilar substrate, and the decrease in crystal defects toward the free-standing substrate surface.

If the number of crystal defects is large, the empty space inside the crystal increases, and the length of the crystal increases, and if the crystal defect is small, the empty space inside the crystal decreases, so that the length of the crystal is relatively smaller than that of many crystal defects. That is, as shown in FIG. 2, a compressive stress is present on the upper surface of the GaN free-standing substrate, and the GaN free-standing substrate is convexly convex toward the heterogeneous substrate, and the surface is concave. have.

If the substrate is bent, the yield of the thin film growth process or the photolithography process, which is essential for the device manufacturing process, is greatly reduced. That is, in order to manufacture the GaN free-standing substrate, a technique for controlling the warpage of the substrate is required. Conventional GaN self-supporting substrate bending control technology used a method to make the flattened surface of the curved GaN crystal through the machining process as shown in FIG. The GaN free-standing substrate prepared in this manner has a seemingly flat shape, but exists in a crystallographically curved state. When manufacturing a device by growing a GaN thin film or the like on the existing GaN free-standing substrate, a crystallographically curved thin film is obtained and the quality of the thin film is non-uniform, thereby resulting in non-uniform device performance. It causes falling.

Accordingly, an object of the present invention is to provide a method of manufacturing a GaN free-standing substrate by growing a GaN thick film crystallized from warpage.

First, to summarize the features of the present invention, the gallium nitride self-supporting substrate manufacturing method according to an aspect of the present invention, by supplying GaCl gas and NH ₃ gas in a predetermined ratio in a heated reactor to form a GaN crystal to the substrate in the reactor Growing to a certain time; And reducing the supply amount of the NH ₃ gas to a predetermined ratio relative to the initial supply amount after the predetermined time, and in the reducing step, the supply amount of the NH ₃ gas as the GaN crystal thickness grown on the substrate is increased. It is characterized in that for increasing the nitrogen vacancies in the GaN crystal by reducing the.

The nitrogen vacancies induce an increase in the crystal lattice constant with increasing GaN crystal thickness so that the surface tensile stress cancels out the compressive stress on the substrate. To grow.

In the reducing step, the supply amount of the NH ₃ gas may be reduced by 1/10 to 9/10 of the initial supply amount. It is possible to reduce the supply amount of the NH ₃ gas over a plurality of stages at regular time intervals.

When the GaN crystals are grown to a thickness of 1.0 to 1000 μm for the predetermined time on the substrate, the reducing may be performed.

Prior to the growing, the surface of the charged substrate may further comprise nitriding with NH ₃ gas in the heated reactor.

The method may further include supplying a corresponding gas to the reactor for dopant doping while the GaN crystals are grown in the growing or decreasing.

According to the method for manufacturing a GaN free-standing substrate according to the present invention, the compressive stress caused by the reduction of crystal defects such as dislocations with increasing thickness of the GaN thick film is offset by the tensile stress artificially produced by gradually reducing the nitrogen source gas. By doing so, it is possible to produce a GaN free-standing substrate which is not crystallographically warped.

In addition, when ammonia gas, which is a nitrogen source, is gradually reduced to obtain a GaN free-standing substrate that is not crystallographically warped, lateral growth is promoted by increasing the diffusion movement distance of Ga atoms at the interface where crystal growth occurs. It is possible to improve the quality of the substrate by reducing the occurrence of crystal defects such as pit).

In addition, when the thin film is grown on the GaN freestanding substrate, which is not crystallographically, it is possible to obtain uniform properties of the thin film. Thus, when the device is manufactured from the thin film grown on the GaN freestanding substrate, a device having uniform properties can be obtained. The device manufacturing yield can be improved.

1 is a structural diagram of a general HVPE device.
FIG. 2 is a diagram illustrating a warpage phenomenon due to crystal defects in a general GaN freestanding substrate.
3 is a view for explaining a polishing process of a general GaN freestanding substrate having warpage.
4 is a flowchart illustrating a GaN freestanding substrate manufacturing method according to an embodiment of the present invention.
FIG. 5 is a view for explaining a GaN thick film growth process without warpage by canceling the compressive stress due to crystal defects in the manufacturing process of FIG. 4 with tensile stress due to nitrogen vacancies.
6 is a view for explaining the change in the GaN lattice constant according to the nitrogen vacancies concentration in the manufacturing process of FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

4 is a flowchart illustrating a GaN freestanding substrate manufacturing method according to an embodiment of the present invention.

First, a substrate (for example, sapphire substrate) is charged to the reactor of the HVPE growth apparatus as shown in FIG. 1 (S10). In some cases, a substrate made of another material such as SiC, GaAs, Si, GaN may be used instead of the sapphire substrate. The reactor of the HVPE growth apparatus is divided into a source zone where raw materials are supplied and a growth zone where growth occurs. The source zone includes a boat containing Ga metal. Under the control of the gas supply connected to the gas cabinet, a NH ₃ supply tube, an HCl supply tube for reacting with Ga metal to generate GaCl, and a dopant supply tube for doping You will get the gas you need.

Thereafter, the atmosphere temperature of the growth zone of the reactor is heated to 950-1100 ° C. (eg, 1030 ° C.) using a heating furnace of the HVPE growth apparatus, and the surface of the substrate is nitrided with NH ₃ gas (S20).

Next, GaCl gas and NH ₃ gas are supplied onto the nitrided substrate to grow a GaN thick film (S30). To this end, in order to supply GaCl gas and NH ₃ gas on the substrate, NH ₃ , HCl and the like are supplied through the gas supply tube as described above.In the beginning, the ratio of Ga atoms and nitrogen (N) atoms in the GaN crystal is 1: 1. The gas is supplied by adjusting the ratio of the GaCl gas, which is Ga raw material, and the NH ₃ gas, which is a raw material of nitrogen, to be near. For example, according to the reactor structure of the HVPE growth apparatus, the ratio of supply of GaCl gas, which is a Ga material, and NH ₃ gas, which is a source of nitrogen, is 1: 1 to 1:20, for example, Ga atoms and nitrogen in the GaN crystal. N) The ratio of atoms can be around 1: 1. For example, by supplying 200 sccm of GaCl gas, which is a Ga raw material, and 2000 sccm of NH ₃ gas, which is a raw material of nitrogen, a ratio of Ga atoms and nitrogen (N) atoms in a grown GaN crystal is about 1: 1. That is, the ratio of GaCl and NH ₃ can be sufficiently supplied at 1:10. At this time, at a constant growth rate (eg, 100 μm / hr) and growing for a predetermined time (eg, 3 hours), the thickness of the GaN thick film to be grown becomes a constant thickness (eg, 300 μm) of 1.0 to 1000 μm. .

When GaN is grown on the nitrided substrate as described above for a predetermined time and a GaN thick film having a predetermined thickness (eg, 300 μm) or more is grown (S40), the supply of NH ₃ gas is then 1/10 to the initial supply amount. It gradually decreases to 9/10 to increase nitrogen vacancies in the GaN crystal (S50). For example, sikidoe gradually decreases the supply of the NH ₃ gas to the supply amount from the first half of 1000sccm 2000sccm, a certain amount of time (e.g., 30 minutes) to a supply amount of the NH ₃ gas in stages by a predetermined amount (for example, 200sccm) Can be reduced. When the supply amount of NH ₃ gas is reduced to a predetermined 1000 sccm, growth of GaN may be continued for a suitable time (eg, 30 minutes), and then the growth may be terminated by stopping the supply of gas such as NH ₃ , HCl. By increasing the nitrogen vacancies in the GaN crystal as the GaN crystal thickness increases, the GaN thick film which can be convex toward the substrate due to the compressive stress caused by the crystal defect in the GaN crystal on the substrate side is obtained. It is offset by the tensile stress (surface stress) on the surface can form a thick film having a GaN crystal crystallographically unbending as shown in FIG.

In this case, if GaN is grown in the steps S30 and S50 as necessary, the grown GaN thick film may be doped with a predetermined dopant by supplying necessary gases to the reactor through a dopant supply tube. For example, GaN grown through supply of a corresponding gas during GaN crystal growth may be doped with Si, Mg, Fe, Zn, or the like.

When the formation of the grown GaN thick film is completed, the substrate is taken out of the HVPE growth apparatus, and the GaN thick film separated through a substrate separation process of separating the grown GaN thick film from the substrate, that is, crystallographically free from warpage. A GaN free-standing substrate is obtained and properly processed (S60). A spontaneous substrate separation method may be used to obtain a GaN freestanding substrate. For example, the obtained GaN free-standing substrate is mounted on a circular processing apparatus and circularly processed into a wafer shape having a desired diameter. The crystal orientation measuring device can measure the grown GaN crystal surface such as the (11-20) plane and process the orientation display surface, round the corners of the GaN independent substrate, and wrap and free the surface of the GaN independent substrate. Pre-polishing and polishing may be performed to complete the mirror-finished GaN freestanding substrate.

In more detail with respect to the above step S50, GaN single crystal is composed of Ga atoms and N atoms, the lattice constant (lattice constant) is changed as shown in Fig. 6 in accordance with the ratio of Ga and N. A graph of the lattice constant according to the ratio of Ga and N of FIG. 6 is extracted from the document "Gallium Nitride (GaN) II, Volume Editions, Jacques I. Pankove, SEMICONDUCTORS AND SEMIMETALS vol. 57" It is well known.

As shown in FIG. 6, as the V / III group ratio increases from 0 to 2000, the lattice constant of the crystal c-axis decreases from 0.5192 to 0.5182. In other words, it is known that the GaN lattice constant change when the N constituting GaN is not sufficient and when the N is sufficient is changed by about 1%. As the N is sufficiently supplied, the lattice constant of the c-axis decreases, and the closer to the lattice constant of the ideal GaN crystal. Therefore, when the amount of Ga becomes larger than N, the length of the lattice constant increases. The reason is that as the nitrogen vacancy increases, the space where Ga and nitrogen do not bond increases, so that the interval between atoms constituting the crystal becomes wider and the lattice constant increases. This principle has been used in the present invention.

That is, in the initial stage of GaN thick film growth, GaCl gas, which is a raw material of Ga, and NH ₃ gas, which is a raw material of N, are adjusted so that the ratio of Ga atoms and nitrogen (N) atoms in the crystal is about 1: 1. That is, typically the ratio of Ga and N of 1: sufficiently supply the NH ₃ to 2 or more. As the thickness of the crystal increases, the nitrogen vacancy gradually increases in the grown GaN single crystal by gradually reducing the NH ₃ gas supply, and the crystal lattice constant increases as the thickness of the crystal increases. At the end of GaN thick film growth, NH ₃ gas, a raw material of nitrogen, is reduced to less than 9/10 of the supply amount of NH ₃ gas at the beginning of growth.

The GaN thick film grown in this manner increases the lattice constant from the bottom to the top as the thickness increases, so that a tensile stress is formed on the GaN thick film surface. This artificially created tensile stress is offset by the compressive stress caused by the defect of the GaN thick film, resulting in a free GaN free substrate.

As described above, when the thickness increases as the GaN thick film grows, crystal defects such as dislocations decrease with increasing thickness, and compressive stress due to crystal defects occurs in the GaN crystal on the substrate side. When the GaN free-standing substrate is manufactured in the present state, the GaN free-standing substrate is not bent in appearance, but is crystallographically bent. In order to remove such compressive stress, in the present invention, when the GaN thick film grows, the nitrogen source gas is gradually reduced when the thickness becomes more than a certain thickness, thereby increasing the nitrogen vacancies in the crystal with increasing thickness, resulting in crystal lattice constant due to nitrogen vacancies. Since the tensile stress is artificially formed on the surface of the GaN free-standing substrate, the compressive stress is canceled, thereby making it possible to produce a crystallographically uneven GaN free-standing substrate having reduced crystal defects.

Although the above description was made mainly on the method of HVPE (Hydride Vapor Phase Epitaxy), the method of manufacturing a gallium nitride independence board of the present invention may include various methods such as metalorganic vapor phase epitaxy (MOCVD) and molecular beam epitaxy (MBE). It can also be done through a growth device.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

Hydrochloride Vapor Phase Epitaxy (HVPE)
Tensile stress
Compressive stress

Claims (7)

Supplying GaCl gas and NH ₃ gas at a predetermined ratio into the heated reactor to grow GaN crystals on the substrate in the reactor to a predetermined time; And
Reducing the supply amount of the NH ₃ gas to a ratio relative to the initial supply amount after the predetermined time;
In the reducing step, to increase the nitrogen vacancies in the GaN crystals by reducing the supply amount of the NH ₃ gas as the GaN crystal thickness grown on the substrate increases,
Before the growing step, further comprising nitriding the surface of the loaded substrate with NH ₃ gas in the heated reactor. The method of claim 1,
The gallium nitride independence board manufacturing method of claim 1, wherein the nitrogen vacancies induce an increase in the crystal lattice constant as the GaN crystal thickness increases, and thus the surface tensile stress cancels the compressive stress toward the substrate. Way. The method of claim 1,
In the reducing step,
The method of manufacturing a gallium nitride independence board, characterized in that for reducing the supply amount of the NH ₃ gas to 1/10 ~ 9/10 compared to the initial supply. The method of claim 3,
The gallium nitride independence board manufacturing method characterized in that the supply amount of the NH ₃ gas is reduced over a plurality of steps at regular time intervals. The method of claim 1,
If the GaN crystals are grown to 1.0 ~ 1000㎛ thickness for the predetermined time on the substrate, characterized in that the step of reducing the gallium nitride independence board manufacturing method. delete The method of claim 1,
Supplying the gas to the reactor for dopant doping while the GaN crystals are grown in the growing or reducing step
Gallium nitride self-supporting substrate manufacturing method comprising a further.

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