TWI728681B - Substrate for MOCVD and method for growing buffer layer on the substrate - Google Patents

Abstract

The present invention provides a substrate for MOCVD, wherein the upper surface of the substrate includes a central area and an edge area, the edge area surrounds the central area, wherein the central area is composed of single crystal structure alumina, and the surface is smooth, and the edge area The surface is rough, so that when the substrate is fed into the MOCVD reaction chamber, a buffer layer with a single crystal structure is grown in the central area, and a buffer layer with a polycrystalline structure is grown in the edge area. During the growth of the buffer layer, the cracks appearing in the buffer layer of the polycrystalline structure in the edge region will not extend along the lattice structure to the buffer layer of the single crystal structure in the middle region, which greatly improves the production efficiency of semiconductor devices.

Description

Substrate for MOCVD and method for growing buffer layer on the substrate

The present invention relates to the field of semiconductor processing, in particular to a substrate for metal organic chemical vapor deposition (MOCVD) and a method for processing the substrate to form a buffer layer.

The MOCVD process is widely used to manufacture semiconductor components such as LED chips and power components. The structure diagram of the MOCVD reactor includes a reaction chamber 100 as shown in FIG. 1. The bottom of the reaction chamber 100 includes a tray 110 on which one or more substrates 10 to be processed are placed. The bottom of the tray is driven to rotate by a driving device such as a rotating shaft 112, and a heater 114 is provided below the tray 110, so that the tray 110 is heated to a required temperature (600-1200 degrees). The heater 114 and the rotating shaft 112 are surrounded by a side wall 113 to reduce heat radiation to the surroundings and also prevent the reaction gas from entering under the tray 110. The top of the reaction chamber 100 includes a top cover 200, and the top cover 200 includes a gas shower head for supplying a variety of reaction gases downward. The gas shower head includes a plurality of gas diffusion chambers 201 and 202 which are gas-isolated from each other. Different reaction gases, such as metal organic gases, are introduced into the reaction space above the tray 110 in the reaction chamber 100 through respective gas pipes 211 and 212. (TMG) and nitrogen-containing gas (NH ₃ ) finally form the desired compound on the substrate 10, such as gallium nitride GaN. The gas shower head further includes a coolant pipe 205 connected to a coolant source to cool the gas shower head. The semiconductor material layer used to form the LED element is usually composed of crystalline gallium nitride, but the substrate material commonly used in the prior art is usually composed of crystalline aluminum oxide (Al ₂ O ₃ ). The crystal structure between the two is very different, and the crystal lattice is not matched. Therefore, it is necessary to grow a multi-layer buffer layer on the substrate to finally grow the GaN material layer needed to produce the LED. In the prior art, the buffer layer is usually an aluminum nitride AlN layer. However _{, due to lattice mismatch when growing AlN on the sapphire (Al 2} O ₃ ) substrate at a high temperature, the thickness of the buffer layer gradually increases. A large amount of stress is generated, and when AlN grows to a certain thickness, cracks will occur. The cracks are first generated from the edge of the substrate and extend to the center. The existence of cracks makes the AlN film unsuitable for the next step of component structure growth, so the growth must be suppressed The occurrence of cracks. Figure 2 shows the cracks displayed after scanning the AlN film on the substrate with the instrument. Each line represents a crack. So many cracks cause the semiconductor structure above to fail to grow effectively. The components generated on the processing area are scrapped; therefore, the conventional technology needs to provide a new device or growth process to overcome the large number of cracks that occur during the growth of the buffer layer AlN, so as to improve the production quality and yield of LED components.

In view of this, the purpose of the present invention is to provide a device or a special process that prevents serious cracking during the process of growing a thicker buffer layer on a sapphire substrate used for MOCVD.

The present invention proposes a substrate for MOCVD. The upper surface of the substrate includes a central area and an edge area. The edge area surrounds the central area. The central area is composed of single crystal structure aluminum oxide and has a smooth surface. The surface is rough, so that when the substrate is fed into the MOCVD reaction chamber, a buffer layer with a single crystal structure is grown in the central area, and a buffer layer with a polycrystalline structure is grown in the edge area.

Further, the width of the edge area of the substrate is less than 4 mm, wherein the surface roughness of the central area is less than 1 nm, and the surface roughness of the edge area is greater than or equal to 5 nm.

The present invention further provides a substrate for MOCVD. The upper surface of the substrate includes a central area and an edge area, the edge area surrounds the central area, and the edge of the substrate includes a A step, the height of the upper surface of the step is lower than the height of the upper surface of the central area, an auxiliary ring is arranged on the step, and the upper surface of the auxiliary ring has a different roughness or material from the central area. The auxiliary ring can also be made of alumina, and the roughness of the upper surface is greater than that of the central area, or the auxiliary ring can also be made of silicon carbide.

The present invention further provides a MOCVD processor. The processor includes a substrate tray, a heater is arranged below the substrate tray, and a reactive gas inlet device is provided above the substrate tray to pass various reactive gases downward. The substrate tray is provided with a substrate with a smooth and rough edge in the central area, the reaction gas inlet device passes the reaction gas into the substrate to form a buffer layer, wherein the buffer layer grown in the central area of the substrate is a single crystal Structure, the buffer layer grown in the edge area of the substrate has a polycrystalline structure.

The present invention further provides a method for growing a buffer layer on a substrate, including: providing an initial substrate having a single crystal alumina crystal structure and a smooth surface; and performing pretreatment on the initial substrate to generate a first substrate A thickness of the first buffer layer; processing the substrate on which the first buffer layer is deposited, so that the first buffer layer in the edge area of the substrate has a higher roughness than the central area of the substrate; after the processing The buffer layer is deposited again on the substrate to generate a second buffer layer with a second thickness, the second thickness being greater than the first thickness; wherein the second buffer layer in the central area of the substrate is a single crystal structure, and the second buffer layer in the edge area of the substrate The buffer layer has a polycrystalline structure.

The present invention further provides another method for growing a buffer layer on a substrate, including: providing an initial substrate having a monocrystalline alumina crystal structure and a smooth surface; and performing the first MOCVD deposition on the initial substrate A process to generate a first buffer layer with a first thickness, wherein the first buffer layer includes an edge region and a central region, and the edge region has a roughness greater than that of the central region; the second MOCVD deposition is performed on the substrate on which the first buffer layer is grown The manufacturing process enables a second buffer layer with a second thickness to be formed on the substrate, wherein the second thickness is greater than the first thickness. In the first MOCVD deposition process, the heating power of the edge area heater in the MOCVD or the position of the movable ring is controlled so that the edge area of the substrate is The temperature of the domain and the temperature of the central area of the substrate have a first temperature difference, and the second temperature difference between the edge area of the substrate and the central area of the substrate in the second MOCVD deposition process is smaller than the first temperature difference.

The above-mentioned buffer layer is composed of aluminum nitride, and a gallium nitride material layer can be grown as a semiconductor element layer after the buffer layer is deposited. The roughness of the edge area is greater than 5 nm, and the roughness of the central area is less than 1 nm.

10, 20: Substrate

11, 20b: rough area

12a, 12b, 22a, 22b: buffer layer

13: steps

14: auxiliary ring

20a: smooth area

100: reaction chamber

110: Pallet

112: Rotation axis

113: Sidewall

114: heater

200: top cover

201, 202: Gas diffusion chamber

205: Coolant pipe

211,212: Gas pipeline

In order to more clearly describe the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are For some of the embodiments of the present invention, those with ordinary knowledge in the technical field can obtain other drawings based on these drawings without creative work.

Figure 1 is a schematic diagram showing the structure of a conventional MOCVD reactor; Figure 2 is a schematic diagram showing the distribution of cracks on the substrate when a conventional technology is used; Figure 3 is a schematic diagram showing the surface structure of the substrate of the present invention; Figures 4a and 4b show the crystal growth process on the surface of the substrate under the surface structure of the substrate of the present invention.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described here. Those with ordinary knowledge in the technical field may not violate the connotation of the present invention. In the case of similar promotion, the present invention is not limited by the specific embodiments disclosed below.

After research, the inventor found that a large number of cracks in the growth process of the buffer layer start from the edge area of the substrate and extend along the lattice structure to the central area of the substrate. Therefore, the deposition process using the conventional technology is shown in Figure 2 A large number of cracks distributed in a straight line were generated later. Therefore, in order to greatly reduce the occurrence of cracks, the inventor proposes a substrate structure as shown in Figure 3. The surface of the substrate 10 includes a large area of smooth areas for growing an AlN material layer, and the surface roughness of the smooth areas is less than 1 nm, typically Is 0.2nm. At the same time, a rough area 11 is included in the edge area of the substrate. The roughness of the upper surface of the substrate in the rough area 11 makes it impossible to effectively grow a smooth AlN crystal material layer in the rough area 11. The surface roughness of the substrate in the rough area 11 It is much larger than the central smooth area and can reach 5 nm or more than 10 nm. Such roughness makes the AlN material layer only grow a polycrystalline aluminum nitride material layer in the rough area 11, and cannot form a single crystal structure buffer layer. Because there is no material layer of single crystal structure in the rough area 11 of the edge, even a small amount of cracks in the edge area will not spread along the complex lattice combination of the polycrystalline structure to the smooth area of the center to form long crack bands. Diffusion in a very small area in the edge area. The conventional substrate is usually a circular sheet with a diameter of 2-8 inches, in which the width of the ring-shaped rough area 11 can be set to be very narrow, such as less than 4mm, or even less than 2mm, which is the area discarded in this several millimeter wide endless belt. It will not greatly affect the overall effective growth area, but it can greatly reduce the probability of cracks in the central smooth area. Therefore, although the rough area 11 on the edge cannot be reused to grow the above various semiconductor device structures, it is still possible to achieve far higher production efficiency than the conventional technology to ensure that the smooth area at the center produces high-quality devices.

The rough area 11 located in the edge area of the substrate in the present invention can be made of the substrate 10 and an auxiliary ring 14 fixed on the edge of the substrate as shown in Figure 4a. The outer periphery of the substrate 10 includes a concave step 13. An auxiliary ring 14 is provided on the upper surface of the step. The upper surface of the auxiliary ring 14 has a roughness far greater than the roughness of the upper surface of the center of the substrate 10. After the combination of the substrate 10 and the auxiliary ring 14 are fed into the reaction chamber 100 together, the growth of the buffer material layer (AlN) starts until the buffer layer 12a reaches the target thickness and crystal structure. The buffer layer 12a grown in the smooth area at the center of the substrate 10 has a single crystal structure and has a flat surface. The difference is that the upper surface of the auxiliary ring 14 on the edge of the substrate is very rough, so the buffer layer 12b deposited on the auxiliary ring 14 is not only rough, but also not a single crystal structure but a polycrystalline structure. Although this polycrystalline structure cannot grow an effective semiconductor structure in the subsequent crystal growth process, it can avoid cracks in the subsequent buffer layer growth process. The auxiliary ring 14 can be made of the same aluminum oxide material as the substrate 10, or can be made of other high-temperature resistant materials, such as SiC, as long as it can be fixed on the substrate 10 and the auxiliary ring can be used during the buffer layer growth process. The buffer layer 12a grown on 14 has a different crystal structure from the smooth region in the middle, and any auxiliary ring can be used for the purpose of the present invention. When the material of the auxiliary ring 14 is different from the material of the substrate 10, even if the auxiliary ring 14 is of a single crystal structure, and the surface is very smooth, single crystal AlN cannot be formed. For example, when the auxiliary ring 14 is made of SiC, it is different from the need to grow. The crystalline lattice size gap of the AlN material is too large to form a single crystal structure, and only a polycrystalline structure of AlN can be formed, so it also belongs to one of the embodiments of the present invention.

The present invention further provides another embodiment for generating rough areas 11 in the edge area of the substrate. As shown in Figure 4b, pre-processing is first performed on the flat substrate 20 to make the edge area of the substrate 20 produce sufficiently rough areas. The pretreatment may be mechanical processing at the edge or chemical treatment. The surface of the substrate is corroded by reactive gas or liquid at the edge to form a rough area 20b surrounding the smooth area 20a at the center of the substrate. Subsequently, a buffer layer growth process is performed to grow a single crystal, smooth buffer layer 22a on the central smooth area 20a, and at the same time grow a rough surface, polycrystalline buffer layer 22b on the rough area 20b.

In order to achieve the purpose of the present invention, a dedicated substrate with rough edges as shown in Figure 4a and Figure 4b can be selected, or a traditional substrate with a smooth upper surface can be used to initially grow a certain thickness of buffer on the substrate. Before a large number of cracks appear, the substrate is taken out to roughen the edges, and then sent to the MOCVD reactor for subsequent buffer layer growth until the target thickness is reached, and finally the semiconductor structure material layer is grown on the substrate.

For MOCVD reactors with only one substrate on the substrate tray, the growth effect on the substrate can be further changed by changing the airflow or the temperature distribution around the tray. In the initial growth process of the buffer layer, the first MOCVD growth process is performed to deliberately grow an initial buffer layer with a smooth center area and rough edges, and then a second MOCVD growth process is performed to grow a complete buffer layer in the center of the substrate. The buffer layer of the required thickness and structure. The thickness of the initial buffer layer is smaller than the thickness of the buffer layer grown in the second MOCVD growth process. The above-mentioned reactor structure that deliberately generates a rough layer on the edge can be the structure described in the patent CN201820837091.8 filed by the applicant of the present invention. A liftable baffle is arranged around the substrate tray, and when the initial buffer layer is grown When the baffle is lowered, a large amount of heat in the edge area of the substrate tray is radiated to the low temperature reaction chamber area. The temperature of the edge of the substrate tray will be significantly lower than the central area, so the edge area of the substrate tray has a lower temperature and can only grow amorphous The buffer layer. On the other hand, the present invention can also control the heating power distribution of the heater 114 in order to achieve the purpose of achieving the edge area whose temperature is significantly lower than the central area. The heater includes a plurality of independently controlled areas. The power is less than the power of the heating wire in the center or the middle area, so the temperature of the extreme edge area of the substrate tray will be much lower than the center or middle area, which will eventually make the polycrystalline material layer deposited and produced in the edge area of the substrate have high roughness, and the central area forms a single The crystalline material layer has a smooth surface.

The above are only the preferred embodiments of the present invention. Although the present invention has been disclosed as above in preferred embodiments, it is not intended to limit the present invention. Anyone familiar with the general knowledge in the technical field, without departing from the scope of the technical solution of the present invention, can use the methods and technical content disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify into equivalent changes. Equivalent embodiment. Therefore, all simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall within the protection scope of the technical solution of the present invention.

10: Substrate

11: rough area

Claims (12)

A substrate for MOCVD, wherein the upper surface of the substrate includes a central area and an edge area, the edge area surrounds the central area, wherein the central area is composed of single crystal structure alumina, and the surface is smooth, the edge The surface of the area is rough, so that when the substrate is fed into the MOCVD reaction chamber, a buffer layer with a single crystal structure is grown in the central area, and a buffer layer with a polycrystalline structure is grown in the edge area. The substrate according to claim 1, wherein the width of the edge area of the substrate is less than 4 mm. The substrate according to claim 1, wherein the surface roughness of the central area is less than 1 nm, and the surface roughness of the edge area is greater than or equal to 5 nm. A substrate for MOCVD, wherein the upper surface of the substrate includes a central area and an edge area, the edge area surrounds the central area, the edge of the substrate includes a step, and the height of the upper surface of the step is lower than the central area An auxiliary ring is set on the step, and the upper surface of the auxiliary ring has a different roughness or material from the central area. The substrate according to claim 4, wherein the roughness of the upper surface of the auxiliary ring is greater than the roughness of the central area. The substrate according to claim 4, wherein the auxiliary ring is made of silicon carbide. A MOCVD processor, wherein the processor includes a substrate tray, a heater is arranged below the substrate tray, and a reactive gas inlet device is provided above the substrate tray to pass various reactive gases downward. The tray is provided with the substrate as described in claim 1 or 4, the reaction gas inlet device passes the reaction gas into the substrate to form a buffer layer, wherein the buffer layer grown in the central area of the substrate has a single crystal structure , The buffer layer grown in the edge area of the substrate is polycrystalline Structure. A method for growing a buffer layer on a substrate includes: providing an initial substrate having a monocrystalline alumina crystal structure and a smooth surface; and preprocessing the initial substrate to generate a first thickness of a first substrate. Buffer layer; processing the substrate on which the first buffer layer is deposited, so that the first buffer layer in the edge area of the substrate has a higher roughness than the central area of the substrate; the substrate after the treatment The buffer layer is deposited again on the chip to generate a second buffer layer with a second thickness, the second thickness being greater than the first thickness; wherein the second buffer layer in the central area of the substrate has a single crystal structure, and the edge of the substrate The second buffer layer in the region has a polycrystalline structure. A method for growing a buffer layer on a substrate includes: providing an initial substrate having a monocrystalline alumina crystal structure and a smooth surface; performing a first MOCVD deposition process on the initial substrate to generate a first thickness A first buffer layer of, wherein the first buffer layer includes an edge area and a central area, the edge area has a roughness greater than the central area; a second MOCVD is performed on the substrate on which the first buffer layer is grown The deposition process generates a second buffer layer with a second thickness on the substrate, wherein the second thickness is greater than the first thickness. The method for growing a buffer layer on a substrate according to claim 8 or 9, wherein the buffer layer is made of aluminum nitride. The method for growing a buffer layer on a substrate as described in claim 8 or 9, wherein the The roughness of the edge area is greater than 5 nm, and the roughness of the central area is less than 1 nm. The method for growing a buffer layer on a substrate according to claim 9, wherein in the first MOCVD deposition process, the heating power of an edge area heater in MOCVD is controlled or the position of an auxiliary ring can be moved so that the substrate is The temperature of the edge area and the temperature of the central area of the substrate have a first temperature difference, and in the second MOCVD deposition process, the edge area of the substrate and the central area of the substrate have a second temperature The difference is less than the first temperature difference.

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