CN111719136A

CN111719136A - Substrate for MOCVD and method for growing buffer layer on substrate

Info

Publication number: CN111719136A
Application number: CN201910217948.5A
Authority: CN
Inventors: 李洪伟; 胡建正; 王文; 郭世平
Original assignee: Advanced Micro Fabrication Equipment Inc Shanghai
Current assignee: Advanced Micro Fabrication Equipment Inc Shanghai; Advanced Micro Fabrication Equipment Inc
Priority date: 2019-03-21
Filing date: 2019-03-21
Publication date: 2020-09-29
Also published as: TW202039915A; TWI728681B

Abstract

The invention provides a substrate for MOCVD, which is characterized in that the upper surface of the substrate comprises a central region and an edge region, wherein the edge region surrounds the central region, the central region is made of alumina with a single crystal structure, the surface of the central region is smooth, the surface of the edge region is rough, so that when the substrate is fed into an MOCVD reaction chamber, a buffer layer with a single crystal structure grows in the central region, and a buffer layer with a polycrystalline structure grows in the edge region. In the growth process of the buffer layer, cracks appearing in the buffer layer of the edge region polycrystalline structure cannot extend into the buffer layer of the middle region single crystal structure along the lattice structure, and the production efficiency of the semiconductor device is greatly improved.

Description

Substrate for MOCVD and method for growing buffer layer on substrate

Technical Field

The present invention relates to the field of semiconductor processing, and more particularly to a substrate for Metal Organic Chemical Vapor Deposition (MOCVD) and a method of processing on the substrate to form a buffer layer.

Background

MOCVD is widely used for manufacturing semiconductor devices such as LED chips and power devices. The MOCVD tool is shown in fig. 1 and includes a reaction chamber 100, a tray 110 disposed at the bottom of the reaction chamber, and one or more substrates 10 to be processed are placed on the tray. The lower part 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 desired temperature (600-. The heater 114 and the rotary shaft 112 are surrounded by a sidewall 113 to reduce heat radiation to the surroundings and also to prevent the reaction gas from entering below the tray 110. The reaction chamber includes a top cover 200 at the top thereof, and a gas shower head for supplying a plurality of reaction gases downward therein. The gas shower head includes a plurality of

gas diffusion chambers

201, 202, which are gas-isolated from each other, and different reaction gases, such as metal organic gas (TMG) and nitrogen-containing gas (NH3), are respectively introduced into the reaction space above the tray 110 in the reaction chamber through

respective gas pipes

211, 212 to finally form a desired compound, such as GaN. The showerhead also includes a coolant line 205 that communicates with a coolant source to cool the showerhead. The layers of semiconductor material used to form LED devices are typically composed of crystalline gallium nitride, but the substrate material commonly used in the art is typically composed of crystalline aluminum oxide (Al2O 3). The difference of crystal structures between the two is huge, and the crystal lattices are not matched, so that a plurality of buffer layers need to be grown on the substrate firstly to finally grow the GaN material layer required by the LED production. In the prior art, a buffer layer is usually an aluminum nitride (AlN) layer, but when AlN is epitaxially grown on a sapphire (Al2O3) substrate at a high temperature, due to lattice mismatch, a great stress is generated in the buffer layer in the process of gradually increasing the thickness of the buffer layer, and when AlN grows to a certain thickness, cracks are generated, extend from the edge of a substrate to the center, and are not suitable for the next device structure growth due to the existence of the cracks, so that the generation of the cracks during growth must be inhibited; there is therefore a need in the art to provide a new apparatus or growth process to overcome the large number of cracks that occur during growth of the buffer layer AlN to improve LED device production quality and yield.

Disclosure of Invention

In view of the above, the present invention provides a device or a special process that does not cause severe cracking during the growth of a thick buffer layer on a sapphire substrate for MOCVD.

The invention provides a substrate for MOCVD, wherein the upper surface of the substrate comprises a central region and an edge region, the edge region surrounds the central region, the central region is made of alumina with a single crystal structure, the surface of the central region is smooth, the surface of the edge region is rough, so that when the substrate is fed into an MOCVD reaction chamber, a buffer layer with a single crystal structure grows in the central region, and a polycrystalline buffer layer grows in the edge region.

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

The invention also provides a substrate for MOCVD, the upper surface of the substrate comprises a central region and an edge region, the edge region surrounds the central region, the edge of the substrate comprises a step part, the upper surface of the step part is lower than that of the central region, an auxiliary ring is arranged on the step part, and the upper surface of the auxiliary ring has different roughness or material from that of the central region. Wherein the auxiliary ring may also be made of alumina, the upper surface having a roughness greater than that of the central region, or the auxiliary ring may also be made of silicon carbide.

The invention also provides an MOCVD (metal organic chemical vapor deposition) processor, which comprises a substrate tray, wherein a heater is arranged below the substrate tray, a reaction gas inlet device is arranged above the substrate tray and is used for introducing various reaction gases downwards, a substrate with a smooth central area and a rough edge area is arranged on the substrate tray, and the reaction gas inlet device is used for introducing the reaction gases to the substrate to form a buffer layer, wherein the buffer layer grown in the central area of the substrate is of a single crystal structure, and the buffer layer grown in the edge area of the substrate is of a polycrystalline structure.

The invention also provides a method for growing a buffer layer on a substrate, which comprises the following steps: providing an initial substrate, wherein the substrate has a single crystal alumina crystal structure and a smooth surface; preprocessing the initial substrate to generate a first buffer layer with a first thickness; processing the substrate deposited with the first buffer layer, so that the first buffer layer at the edge area of the substrate has higher roughness than the central area of the substrate; depositing the buffer layer on the processed substrate again to generate a second buffer layer with a second thickness, wherein the second thickness is larger than the first thickness; the second buffer layer in the central area of the substrate is of a single crystal structure, and the second buffer layer in the edge area of the substrate is of a polycrystalline structure.

The present invention also provides another method of growing a buffer layer on a substrate, comprising: providing an initial substrate, wherein the substrate has a single crystal alumina crystal structure and a smooth surface; carrying out a first MOCVD deposition process on the initial substrate to generate a first buffer layer with a first thickness, wherein the first buffer layer comprises an edge region and a central region, and the roughness of the edge region is greater than that of the central region; and carrying out a second MOCVD deposition process on the substrate on which the first buffer layer grows, so that a second buffer layer with a second thickness is generated on the substrate, wherein the second thickness is larger than the first thickness. In the first MOCVD deposition process, the heating power of a heater in the edge area or the position of the movable ring in MOCVD is controlled, so that the temperature of the edge area of the substrate and the temperature of the central area of the substrate have a first temperature difference, and in the second MOCVD deposition process, the second temperature difference between the edge area of the substrate and the central area of the substrate is smaller than the first temperature difference.

Wherein the buffer layer is composed of aluminum nitride, and a gallium nitride material layer can be grown as a semiconductor device layer after the buffer layer deposition is completed. The roughness of the edge area is more than 5nm, and the roughness of the central area is less than 1 nm.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 shows a schematic diagram of a prior art MOCVD reactor configuration;

FIG. 2 is a schematic illustration of a crack distribution on a substrate using a prior art process;

FIG. 3 shows a schematic view of the surface structure of a substrate according to the present invention;

FIGS. 4a and 4b show the crystal growth process on the surface of the substrate under the surface structure of the substrate according to the present invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

The inventors have studied and found that a large number of cracks during the growth of the buffer layer are initiated from the edge region of the substrate and extend along the lattice structure toward the central region of the substrate, so that a large number of cracks are generated in a straight line after the deposition process of the prior art as shown in fig. 2. Therefore, in order to greatly reduce the generation of cracks, the inventors proposed a substrate structure as shown in fig. 3, in which the surface of the substrate 10 includes a large-area smooth region for growing the AlN material layer, wherein the surface roughness of the smooth region is less than 1nm, typically 0.2 nm. Meanwhile, the edge area of the substrate comprises a rough area 11, the roughness of the upper surface of the substrate in the rough area prevents a smooth AlN crystal material layer from being effectively grown in the area, the roughness of the surface of the substrate in the rough area is far larger than that of the central smooth area and can reach 5nm or more than 10nm, and the AlN crystal material layer can only grow an aluminum nitride material layer with a polycrystalline structure in the rough area due to the roughness and cannot form a buffer layer with a single crystal structure. Since the rough region of the edge is not provided with the material layer of the single crystal structure, even if a small amount of cracks exist in the edge region, the cracks do not spread to form a long crack zone along the complex lattice combination of the polycrystalline structure to the smooth region in the center, and only spread in a very small area in the edge region. The conventional substrate is typically a circular sheet of 2-8 inches in diameter, wherein the width of the edge annular roughened region 11 can be set very narrow, such as less than 4mm, or even less than 2mm, and the area discarded in this several mm wide annular band does not significantly affect the overall effective growth area, but can significantly reduce the probability of cracking in the central smooth region. Therefore, although the rough region 11 at the edge can not be used for growing various semiconductor device structures above, the device with high quality produced by ensuring the smooth region at the center can still achieve much higher production efficiency than the prior art.

The roughened region 11 of the present invention, which is located at the edge region of the substrate, can be made of the substrate 10 and an auxiliary ring 14 attached to the edge of the substrate as shown in fig. 4 a. Wherein the outer periphery of the substrate 10 includes a recessed step 13, and an auxiliary ring 14 is disposed on the upper surface of the step, and the roughness of the upper surface of the auxiliary ring is much larger than that of the central upper surface of the substrate 10. Growth of the buffer material layer (AlN) is started after the combination of the substrate 10 and the auxiliary ring 14 is fed into the reaction chamber together until the buffer layer 12 reaches a target thickness and crystal structure. In contrast to the buffer layer 12a, in which the central smooth region of the substrate 10 is grown, having a single crystal structure and a smooth surface, the upper surface of the auxiliary ring 14 at the edge of the substrate is rough so that the buffer material layer 12b deposited on the auxiliary ring 14 is not only rough in surface but also not of a single crystal structure but of a polycrystalline structure. Although the polycrystalline structure cannot grow an effective semiconductor structure in the subsequent crystal growth process, cracks can be avoided in the subsequent buffer layer growth process. The auxiliary ring 14 may be made of the same alumina material as the substrate, or may be made of other materials resistant to high temperature, such as SiC, and any auxiliary ring can be used for the purpose of the present invention as long as it can be fixed on the substrate 10 and the buffer layer grown on the auxiliary ring during the buffer layer growth process has a crystal structure different from that of the intermediate smooth region. If the material of the auxiliary ring is different from the material of the substrate, even if the auxiliary ring is made of a single crystal structure material and has a smooth surface, single crystal AlN cannot be formed, for example, if SiC is used as the auxiliary ring, the lattice size difference from the AlN material to be grown is too large, and a single crystal structure cannot be formed, but only AlN with a polycrystalline structure can be formed, and thus the present invention also belongs to one of the embodiments of the present invention.

The invention also provides for another embodiment of creating a rough area 11 in the edge region of the substrate, as shown in fig. 4b, by first performing a pretreatment on the flat substrate 10, so that the edge region of the substrate 10 creates a sufficiently rough area. The pre-treatment may be mechanical or chemical treatment, and the surface of the substrate is etched with a reactive gas or liquid at the edge to form a rough area 20b surrounding a smooth area 20a located at the center of the substrate. A buffer layer growth process is then performed to grow a single crystal, smooth buffer layer 22a over the central smooth region 20a, while a rough-surfaced, polycrystalline material layer 22b is grown over the rough region 20 b.

In the invention, the substrate with rough edge area shown in fig. 4a and 4b can be selected for achieving the purpose of the invention, or a traditional substrate with smooth upper surface can be adopted, a buffer material layer with a certain thickness is grown on the substrate initially, before a large number of cracks appear, the substrate is taken out to carry out roughening treatment on the edge, then the substrate is sent into the MOCVD reactor again to carry out subsequent buffer layer growth until the target thickness is reached, and finally the semiconductor structure material layer is grown on the substrate.

For an MOCVD reactor having only one substrate on a substrate tray, the growth effect on the substrate can also be changed by changing the gas flow or the temperature distribution around the tray. In the growth process of the initial buffer layer, a first MOCVD growth process is carried out, an initial buffer layer with a smooth central area and rough edge edges is intentionally grown, and then a second MOCVD growth process is carried out to grow a complete buffer layer so as to obtain the buffer layer with the required thickness and structure in the center of the substrate. Wherein the thickness of the initial buffer layer is less than that of the buffer layer grown by the second MOCVD growth process. The reactor structure, which is intended to produce a rough edge layer, may be as described in the prior patent 201820837091.8 filed by the applicant of the present invention, wherein a raised baffle is provided around the substrate tray, and when the initial buffer layer growth is performed, the raised baffle causes a large amount of heat in the edge region of the substrate tray to be radiated to the lower temperature reaction chamber region, and the temperature at the edge of the substrate tray is significantly lower than that in the central region, so that the edge region of the substrate tray is cooler and only the amorphous buffer layer can be grown. On the other hand, the present invention can also control the heating power distribution of the heater 114 for the purpose of achieving the purpose that the temperature of the edge region is significantly lower than that of the central region, the heater comprises a plurality of independently controlled regions, wherein the power of the heating wire in the extreme edge region is lower than that of the central or middle region, so that the temperature of the extreme edge region of the substrate tray is far lower than that of the central or middle region, and finally the roughness of the polycrystalline material layer deposited and produced in the edge region of the substrate is high, and the monocrystalline material layer formed in the central region has a smooth surface.

The foregoing is only a preferred embodiment of the present invention, and although the present invention has been disclosed in the preferred embodiments, it is not intended to limit the present invention. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims

1. A substrate for MOCVD, characterized in that the upper surface of the substrate comprises a central zone and an edge zone, said edge zone surrounding said central zone, wherein the central zone is made of alumina with a single crystal structure and has a smooth surface, and the surface of the edge zone is rough, so that when said substrate is fed into a MOCVD reaction chamber, a buffer layer with a single crystal structure grows in the central zone, and a polycrystalline buffer layer grows in the edge zone.

2. The substrate of claim 1, wherein the width of the edge region of the substrate is less than 4 mm.

3. The substrate of claim 1, wherein the surface roughness of the central region is less than 1nm and the surface roughness of the edge region is 5nm or greater.

4. A substrate for MOCVD, characterized in that an upper surface of the substrate comprises a central region and an edge region, the edge region surrounds the central region, the edge of the substrate comprises a stepped portion, the height of the upper surface of the stepped portion is lower than that of the central region, an auxiliary ring is provided on the stepped portion, and the upper surface of the auxiliary ring has a different roughness or material from that of the central region.

5. The substrate of claim 4, wherein the auxiliary ring has an upper surface with a roughness greater than a roughness of the central region.

6. The substrate of claim 4, wherein the auxiliary ring is made of silicon carbide.

7. An MOCVD (metal organic chemical vapor deposition) processor is characterized by comprising a substrate tray, wherein a heater is arranged below the substrate tray, a reaction gas inlet device is arranged above the substrate tray, a plurality of reaction gases are introduced downwards, the substrate of claim 1 or 4 is arranged on the substrate tray, the reaction gas inlet device introduces the reaction gases to the substrate to form a buffer layer, the buffer layer grown in the central region of the substrate is of a single crystal structure, and the buffer layer grown in the edge region of the substrate is of a polycrystalline structure.

8. A method of growing a buffer layer on a substrate, comprising:

providing an initial substrate, wherein the substrate has a single crystal alumina crystal structure and a smooth surface;

preprocessing the initial substrate to generate a first buffer layer with a first thickness;

processing the substrate deposited with the first buffer layer, so that the first buffer layer at the edge area of the substrate has higher roughness than the central area of the substrate;

depositing the buffer layer on the processed substrate again to generate a second buffer layer with a second thickness, wherein the second thickness is larger than the first thickness;

the second buffer layer in the central area of the substrate is of a single crystal structure, and the second buffer layer in the edge area of the substrate is of a polycrystalline structure.

9. A method of growing a buffer layer on a substrate, comprising:

carrying out a first MOCVD deposition process on the initial substrate to generate a first buffer layer with a first thickness, wherein the first buffer layer comprises an edge region and a central region, and the roughness of the edge region is greater than that of the central region;

and carrying out a second MOCVD deposition process on the substrate on which the first buffer layer grows, so that a second buffer layer with a second thickness is generated on the substrate, wherein the second thickness is larger than the first thickness.

10. A method of growing a buffer layer on a substrate as claimed in claim 8 or 9, wherein the buffer layer is comprised of aluminum nitride.

11. The method of growing a buffer layer on a substrate of claim 8 or 9, wherein the edge region roughness is greater than 5nm and the center region roughness is less than 1 nm.

12. The method of claim 9, wherein in the first MOCVD deposition process, the heating power of the edge zone heater or the position of the movable ring in MOCVD is controlled such that the temperature of the edge zone of the substrate has a first temperature difference with the temperature of the central zone of the substrate, and in the second MOCVD deposition process, the second temperature difference between the edge zone of the substrate and the central zone of the substrate is smaller than the first temperature difference.