CN118039455A - AlN film with high crystal quality and preparation method and application thereof - Google Patents

Abstract

The invention discloses a high-crystal-quality AlN film, and a preparation method and application thereof. The AlN film provided by the invention has the following characteristics: (1) the surface flatness reaches below 0.1 nm; (2) The dislocation density is less than 1.0X10 ⁸cm^‑2. The invention firstly proposes specific graphical preparation of the AlN/substrate, ensures the consistency of lattice symmetry in an AlN epitaxial layer and a die plate surface, carries out AlN controllable lateral epitaxy on the AlN epitaxial layer, realizes a controllable polymerization process of a specific crystal face, greatly reduces crystal column distortion, greatly reduces dislocation proliferation, and thus realizes an AlN film with low dislocation density and flat surface atomic level.

Description

A high-crystal quality AlN film and its preparation method and application

Technical Field

The present invention belongs to the technical field of preparation of group III nitride semiconductors, and specifically relates to a high-crystal-quality AlN film and a preparation method and application thereof, and in particular to a low-dislocation-density AlN film with an atomically flat surface at heteroepitaxial level and a preparation method and application thereof.

Background technique

High-quality AlN has a wide range of applications in ultraviolet optoelectronic devices, electronic devices, filters, and other fields. Using homoepitaxial growth on AlN substrates to achieve high-quality AlN is the best choice for device applications. However, although the preparation of AlN substrates by physical vapor transport (PVT) or the preparation of quasi-homoepitaxial growth by PVT combined with hydride vapor phase epitaxy (HVPE) can achieve the above goals well, it has the disadvantages of high cost, difficulty in scaling up, and inability to achieve large-scale industrial production. The preparation of AlN thin films by heteroepitaxial growth on heterogeneous substrates can solve these problems.

However, due to the large lattice and thermal expansion coefficient mismatch between the most widely used (0001) AlN and the substrate, the AlN films prepared by heteroepitaxial method often have high threading dislocation density (10 ⁹ -10 ¹⁰ cm ^-2 ) and large residual stress; in particular, these threading dislocations usually extend to the active area of the device. These defects can act as non-radiative recombination centers or leakage channels, which have a very adverse effect on device performance (such as efficiency, reliability and life). Therefore, epitaxial preparation of low dislocation density AlN films on heterogeneous substrates is very important for realizing high-performance devices.

At present, there are mainly the following technical routes for preparing (0001) AlN thin films on heterogeneous substrates:

First, adjust the process parameters of low-temperature AlN nucleation and high-temperature AlN epitaxy to reduce the AlN dislocation density;

The second is to grow AlN on a flat heterogeneous substrate by alternating the growth mode (such as alternating low temperature and high temperature multiple times);

The third method is to use a pulsed Group III metal source or Group V source;

Fourth, the AlN lateral epitaxy method based on patterned substrate is adopted;

The fifth is to adopt a method of epitaxial growth or sputtering of AlN on a heterogeneous substrate followed by high temperature annealing treatment.

Although the above methods have improved the crystal quality of AlN films to a certain extent, in order to achieve high-performance devices, it is still necessary to further develop more effective and stable methods to achieve atomically flat AlN films with low dislocation density. Among them, the lateral epitaxial growth method using patterned substrates has a significant effect in improving the quality of AlN crystals, and has high stability and great development potential.

However, since AlN has a P63mc crystal structure, it is very different from various commonly used substrates (such as sapphire). Crystal structure), so that in the process of epitaxial AlN directly through the patterned substrate, there is a transition from the symmetry of the substrate lattice to the six-fold symmetry of AlN. The resulting atomic misalignment will further lead to dislocations in the closing process, fundamentally limiting the space for improving crystal quality.

Summary of the invention

The technical problem to be solved by the present invention is how to overcome the dislocation multiplication during the polymerization process caused by the difference in crystal symmetry between AlN and substrate in lateral epitaxy, so as to prepare an AlN film with low dislocation density and atomically smooth surface.

In order to solve the above technical problems, the present invention proposes for the first time to carry out specific patterning preparation of the AlN/substrate template on the (0001) plane. By growing AlN on a template with a specific patterned array of holes, the lattice symmetry of the AlN epitaxial layer is guaranteed to be consistent with that of the template plane, and controllable lateral epitaxy of AlN is carried out thereon to realize the controllable polymerization process of specific crystal planes, which greatly reduces the distortion of crystal columns and significantly reduces the proliferation of dislocations, thereby realizing an AlN film with low dislocation density and atomically smooth surface.

In a first aspect, the present invention provides an AlN thin film having the following characteristics:

(1) The surface flatness reaches less than 0.1nm;

(2) The dislocation density is less than 1.0×10 ⁸ cm ^-2 .

In a second aspect, the present invention provides a method for preparing an AlN thin film, comprising the following steps:

S1: preparing an AlN layer with a (0001) surface on a substrate to form an AlN/substrate template;

S2: preparing a patterned array of holes on the AlN/substrate template;

S3: Controlling the polymerization process of AlN on the AlN/substrate template having the patterned array holes to obtain the AlN thin film by epitaxy.

In step S1, an AlN layer is prepared on the substrate by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) or physical vapor deposition (PVD). The substrate includes sapphire, SiC, Si and the like.

The thickness of the AlN layer in the AlN/substrate template does not exceed 2000 nm, preferably in the range of 150-1500 nm.

In step S2, the control of the hole shape in the patterned AlN/substrate template is one of the key points of this solution. Through the optimization of the etching process, the hole needs to be strictly controlled to be AlN or/> The crystal plane family and the plane-to-plane angle present the characteristics of 120 degrees (the hole shape shown in Figure 1), which provides a basis for the controllable crystal plane growth in the subsequent epitaxial process.

The periodic arrangement of the patterned array holes is a polygonal array, including any regular periodic arrangement such as a parallelogram, rectangle, square, hexagon, rhombus, etc. A partial patterned array is shown in FIG2 .

The present invention finds that the depth of the patterned array holes is one of the important parameters to ensure the flatness of the AlN film surface. In the further AlN epitaxy process, polycrystalline or amorphous AlN is usually deposited at the bottom of the hole; if the hole depth is shallow, the AlN deposited in the hole will disrupt the overall growth pattern, making it difficult for the AlN film to form an atomically flat surface morphology. Therefore, the depth of the patterned array holes is preferably 150-500nm, preferably 200-350nm.

The present invention finds that matching the appropriate hole arrangement periodicity and hole size is one of the key technologies to reduce the dislocation density in the AlN film. Through experimental verification, the center distance (period) between any two adjacent holes in the patterned array is preferably 600-2000nm, preferably 900-1500nm. The size of the holes in the patterned array is preferably 300-1400nm, preferably 600-900nm.

Through the above control, the edge distance (hole period minus hole size) between any two adjacent holes in the patterned array is achieved in the range of 300-600nm, preferably in the range of 300-450nm, thereby ensuring that during the lateral epitaxy of AlN on the patterned AlN/substrate template, the misfit dislocations located in the non-hole area and originating from the AlN/substrate interface are acted upon by the mirror force, bend toward the air hole generated by the closing, and terminate at the side wall of the air hole, thereby effectively reducing the dislocation density in the AlN film obtained in step S3.

The method for preparing the patterned array holes is as follows: on the AlN/substrate template, a pattern mask is formed by nanoimprinting or photolithography, and then the template is etched or corroded to form the patterned array holes.

In step S3, the control of the polymerization process of AlN on the patterned AlN/substrate template is the second core point of this patent. It is necessary to select specific epitaxial conditions such as growth temperature, growth rate and V/III ratio to ensure that AlN can be maintained in further lateral epitaxy. or/> The crystal plane family completes the polymerization process without generating other growth crystal planes, thereby effectively suppressing the crystal column distortion caused by atomic dislocation during the closing process and reducing the proliferation of dislocations.

Preferably, in the polymerization process control of AlN, the growth temperature is 1150-1400° C., preferably 1200-1300° C.; the growth pressure is 20-200 mbar, preferably 40-100 mbar.

In the epitaxial growth of AlN thin film by MOCVD on the patterned AlN/substrate template of the present invention, the molar flow ratio (V/III ratio) of ammonia (NH ₃ ) to Al source (trimethylaluminum, TMAl) is one of the key technologies for reducing the dislocation density in the AlN thin film. Preferably, the V/III ratio is 200-1500; more preferably, the V/III ratio is 300-800.

The experimental results show that by optimizing the V/III ratio, the AlN lateral epitaxy rate in S3 can be adjusted, so that the misfit dislocations in the non-hole region originating from the AlN/substrate interface can bend more fully toward the air hole. More importantly, by optimizing the V/III ratio, the patterned holes can be proportionally reduced without deformation during the AlN lateral growth (S3). This shows that the orientation of the laterally grown AlN crystal column is effectively controlled and unified, avoiding the twisting and tilting of the crystal column, inhibiting the generation of dislocations during the subsequent crystal column closure process, and thus reducing the dislocation density in the resulting AlN film.

In a third aspect, the present invention provides an optoelectronic device or an electronic device or a filter, comprising the AlN thin film.

The beneficial effects achieved by the present invention are as follows:

The present invention has found that by performing a specific patterning process on the AlN/substrate template of the (0001) surface, the sides of the obtained hexagonal holes correspond to the AlN or/> In the subsequent AlN epitaxial growth controllable crystal plane polymerization process, the crystal column orientation is effectively controlled and unified, avoiding the twisting and tilting of the crystal column, thereby inhibiting the generation of dislocations during the closing of the crystal column; at the same time, through the matching of the hole period and hole size, the misfit dislocations located in the non-hole area and originating from the AlN/substrate interface are bent toward the air hole generated by the closing and terminated at the side wall of the air hole. Finally, an AlN film with low dislocation density and atomically flat surface is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 shows the periodic arrangement of some patterned hole arrays, including (a) a parallelogram array, (b) a square array, (c) a rectangular array, and (d) a hexagonal array.

FIG. 2 is a flow chart of the method for preparing the AlN thin film described in Example 1.

Detailed ways

The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

The present invention specifically provides a method for preparing an AlN film. As shown in FIG2 , the core idea of preparing the AlN film mainly includes three important steps:

S1: preparing an AlN layer with a (0001) surface on a substrate to form an AlN/substrate template;

S2: Prepare specific patterned array holes on AlN/substrate template;

S3: Control the polymerization process of AlN on the AlN/substrate template with patterned array holes to achieve epitaxial growth of AlN films.

The substrate in step S1 includes sapphire, SiC, Si, etc.

Step S1 can be implemented by MOCVD, MBE, HVPE or PVD (physical vapor deposition) and the like. A single method or a combination of multiple methods can be used, preferably MOCVD or PVD.

Among them, the process conditions for preparing AlN/substrate template by MOCVD method are:

The first step is to place the substrate into a MOCVD reaction chamber, control the temperature of the reaction chamber within the range of 800-1050°C, preferably within the range of 930-980°C, introduce _NH3 and TMAl into the reaction chamber, and grow a low-temperature AlN nucleation layer on the substrate with a thickness of 10-30 nm;

The second step is to keep _NH3 in the state of introduction and suspend the introduction of TMA1;

The third step is to raise the temperature of the reaction chamber to 1150-1400° C., preferably 1200-1300° C., introduce TMAl into the reaction chamber, and grow an AlN layer on the AlN nucleation layer, wherein the thickness of the AlN layer does not exceed 2000 nm; preferably 250-500 nm.

Among them, the process conditions for preparing AlN/substrate template by PVD method are:

The substrate is placed in a PVD reaction chamber, the temperature of the reaction chamber is controlled in the range of 300-900°C, more preferably in the range of 500-800°C, Ar gas is introduced to bombard the Al target, and _N2 is introduced to react with it, so as to sputter and deposit AlN on the substrate, the sputtering power is 1000-6000W, more preferably in the range of 2500-4000W, and the thickness of the AlN layer obtained by sputtering is not more than 2000nm; preferably 250-500nm.

Step S2 can form a pattern mask on the AlN/substrate template by nanoimprinting or photolithography, and then perform etching or corrosion to form patterned holes. The periodic arrangement of the holes is a polygonal array, including any regular periodic arrangement such as parallelogram, rectangle, square, hexagon, rhombus, etc.

in:

The shape of the pores is strictly controlled to form AlN or/> Crystal face family.

The hole period is 600-2000nm, preferably 900-1500nm.

The pore size is 300-1400 nm, preferably 600-900 nm.

The hole depth is 150-500 nm, preferably 200-350 nm.

In step S3, the MOCVD method is used to realize the epitaxial growth of the AlN film on the patterned AlN/substrate template.

in:

The growth temperature is 1150-1400°C, preferably 1200-1300°C;

Growth pressure 20-200 mbar, preferably 40-100 mbar;

The V/III ratio is 200-1500, preferably 300-800.

Example 1

This embodiment provides a method for preparing an AlN thin film, which specifically includes the following steps:

Sl: Place a c-plane sapphire substrate in the reaction chamber of a MOCVD device (3×2" Aixtron CCS FP-MOCVD). In an H ₂ atmosphere, raise the growth temperature to 950°C, introduce TMAl and NH ₃ to grow a 15nm thick AlN nucleation layer, then keep the NH ₃ introduction state and stop introducing TMAl; raise the temperature to 1230°C, introduce TMAl, and grow a 250nm thick AlN film. Then stop introducing NH ₃ and TMAl, cool down, and obtain an AlN/sapphire template with a (0001) plane.

S2: Using nanoimprinting and etching process, patterned holes are prepared on the AlN/sapphire template obtained in S1. The nanoimprinting template period is 1000nm, the hole shape is a regular hexagon, and the diameter is 700nm;

After the etching process, patterned holes with a regular hexagonal periodic arrangement (period 1000nm) are obtained on the AlN/sapphire template. The hole shape is circular, with a diameter of 700nm and a depth of 200nm.

S3: Place the patterned AlN/sapphire template in the reaction chamber of the MOCVD equipment (3×2" Aixtron CCS FP-MOCVD). Under _H2 atmosphere, control the reaction chamber pressure to 50 mbar, increase the growth temperature to 1230℃, introduce _NH3 and TMAl, keep the V/III ratio at 600, and pass AlN After the crystal face group polymerization, AlN film was grown epitaxially with a thickness of 3000nm.

Example 2

This embodiment provides a method for preparing an AlN thin film, which specifically includes the following steps:

Sl: Place a c-plane sapphire substrate in the reaction chamber of a PVD device (Naura iTops A230 AlN Sputter System), raise the growth temperature to 650°C, introduce Ar gas and N ₂ with flow rates of 30 sccm and 180 sccm respectively, and sputter at a sputtering power of 3000 W to sputter-deposit an AlN layer of 500 nm thick on the (0001) plane on the sapphire substrate.

S2: Using photolithography and etching processes, patterned holes are prepared on the AlN/sapphire template obtained in S1. The pattern obtained after photolithography is a square periodic arrangement of holes, with a designed period of 1400nm, a regular hexagonal hole shape, and a side length of 700nm. After the etching process, a square periodic arrangement (period of 1400nm) of patterned holes is obtained on the AlN/sapphire template, and the hole shape is a regular hexagon, with a side length of 700nm and a depth of 300nm.

S3: Place the patterned AlN/sapphire template in the reaction chamber of the MOCVD equipment (3×2" Aixtron CCS FP-MOCVD). Under _H2 atmosphere, control the reaction chamber pressure to 50 mbar, increase the growth temperature to 1230℃, introduce _NH3 and TMAl, keep the V/III ratio at 500, and pass AlN After the crystal planes are polymerized, an AlN film is grown epitaxially with a thickness of 3000 nm.

Comparative Example 1

This comparative example provides a method for preparing an AlN epitaxial film, which directly uses a sapphire substrate as a template and has a circular hole shape, and specifically includes the following steps:

S1: directly use the c-plane sapphire substrate as a template and clean it;

S2: Use nanoimprinting and etching process to prepare patterned holes on the sapphire substrate. The mask obtained by nanoimprinting is a regular hexagonal periodic arrangement of holes, with a designed period of 1000nm, a circular hole shape, and a diameter of 700nm;

After the etching process, a regular hexagonal periodic arrangement (period 1000nm) of patterned holes is obtained on the sapphire template. The hole shape is circular, with a diameter of 700nm and a depth of 200nm.

S3: Place a patterned AlN/sapphire template in the reaction chamber of a MOCVD device (3×2" Aixtron CCS FP-MOCVD). Under _H2 atmosphere, control the reaction chamber pressure to 50 mbar, raise the growth temperature to 1230°C, introduce _NH3 and TMAl, maintain the V/III ratio at 600, and epitaxially grow an AlN film with a thickness of 3000 nm.

Effect verification

The AlN films obtained in Example 1, Example 2 and Comparative Example 1 were tested according to the commonly used detection methods in the art:

(1) Atomic force microscopy: The AlN films obtained in Example 1, Example 2 and Comparative Example 1 all have atomically flat surfaces, with a surface flatness of less than 0.1 nm (3 μm×3 μm);

(2) Planar transmission electron microscopy detection:

The dislocation density of the AlN film obtained in Example 1 is 4.2×10 ⁷ cm ^-2 ;

The dislocation density of the AlN film obtained in Example 2 is 4.9×10 ⁷ cm ^-2 ;

The corresponding dislocation density of the AlN film obtained in Comparative Example 1 is 6.5×10 ⁸ cm ^-2 ;

It can be seen from the above test results that compared with Comparative Example 1, Example 1 and Example 2 have significantly lower dislocation density.

Comparative Example 2

The difference from Example 1 is that step S2 is omitted, and the polymerization process of AlN is directly controlled on the AlN/substrate template to obtain the AlN film by epitaxy.

The results show that due to the omission of step S2, the surface flatness of the obtained AlN film is 0.21 nm (3 μm×3 μm); and the dislocation density of the obtained AlN film is 2.3×10 ⁹ cm ^-2 .

Comparative Example 3

The difference from Embodiment 1 is that in step S2, the shape of the patterned array holes is circular.

The results show that due to the inappropriate shape design of the patterned array holes, the subsequent epitaxial process caused multi-faceted competition due to the transition from three-fold symmetry to six-fold symmetry. The surface flatness of the obtained AlN film was 0.17nm (3μm×3μm); the dislocation density of the obtained AlN film was 3.2×10 ⁸ cm ^-2 .

Comparative Example 4

The difference from Example 1 is that in step S2, the depth of the patterned array holes is 80 nm.

The results show that due to the shallow hole depth, it is difficult to form a large enough hole in the AlN film, and the dislocation suppression effect is very poor. The surface flatness of the AlN film is 0.25nm (3μm×3μm), and the dislocation density of the AlN film is 1.2×10 ⁹ cm ^-2 .

Comparative Example 5

The difference from Example 1 is that the period of any two adjacent patterned array holes is 500 nm, and the size of the hole is 250 nm.

The results show that due to the mismatch between the periodic arrangement of the holes and the hole size, the dislocation density in the obtained AlN film is 7.0×10 ⁸ cm ^-2 .

Comparative Example 6

The difference from Example 1 is that in the polymerization process control of AlN, the growth temperature is 1200° C., the growth pressure is 50 mbar, and the V/III ratio is 50.

The results show that due to the inappropriate matching of epitaxial preparation conditions, it is impossible to maintain a single AlN In the case of crystal plane group polymerization, the dislocation density in the obtained AlN film is 2.1×10 ⁸ cm ^-2 .

Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, these modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims (10)

1. An AlN film having the following characteristics: (1) The surface flatness reaches less than 0.1nm; (2) The dislocation density is less than 1.0×10 ⁸ cm ^-2 . 2. The method for preparing the AlN thin film according to claim 1, comprising the following steps: S1: preparing an AlN layer with a (0001) surface on a substrate to form an AlN/substrate template; S2: preparing a patterned array of holes on the AlN/substrate template; S3: Controlling the polymerization process of AlN on the AlN/substrate template having the patterned array holes to obtain the AlN thin film by epitaxy. 3. The method for preparing an AlN thin film according to claim 2, characterized in that: in step S2, the patterned array holes have the following characteristics: or/> Crystal face family; The angle between the faces is 120 degrees. 4 . The method for preparing an AlN thin film according to claim 2 , wherein in step S2 , the periodic arrangement of the patterned array holes is a polygonal array. 5. The method for preparing an AlN thin film according to any one of claims 2 to 4, characterized in that: in step S2, the depth of the patterned array holes is 150-500 nm. 6. The method for preparing an AlN thin film according to any one of claims 2 to 5, characterized in that: in step S2, the edge distance between any two adjacent patterned array holes is 300-600 nm. 7. The method for preparing an AlN thin film according to any one of claims 2 to 6, characterized in that: in step S2, the center distance between any two adjacent patterned array holes is 600-2000 nm; The size of the patterned array holes is 300-1400 nm. 8. The method for preparing an AlN thin film according to any one of claims 3 to 7, characterized in that: in step S3, the polymerization process of AlN is only or/> The family of crystal planes is completed and no other growth crystal planes are generated. 9. The method for preparing an AlN thin film according to claim 8, characterized in that: in step S3, in the control of the AlN polymerization process, the growth temperature is 1150-1400°C, the growth pressure is 20-200 mbar, and the molar flow ratio of ammonia to Al source is 200-1500. 10 . An optoelectronic device, an electronic device or a filter, comprising the AlN thin film according to claim 1 .