High-crystal-quality AlN thin film, and preparation method and application thereof
Patent Information
- Application Number
- CN202211415099.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-11-11
- Publication Date
- 2026-10-27
- Estimated Expiration
- 2042-11-11
AI Technical Summary
[0012]本发明所要解决的技术问题是如何克服侧向外延中因AlN和衬底晶体对称性差异导致的聚合过程中位错增殖，从而制备位错密度低、表面原子级别平整的AlN薄膜
[0035]本发明研究发现，通过对(0001)面的AlN/衬底模板进行特定图形化工艺，所获的六边形孔洞的边对应于AlN的AlN或
晶面族，在后续AlN外延生长可控晶面聚合过程中，晶柱取向受到有效控制和统一，避免了晶柱的扭转和倾斜，进而抑制了晶柱合拢过程中位错的产生；同时，通过孔洞周期及孔洞大小的匹配，使位于非孔洞区、源自AlN/衬底界面处的失配位错向合拢产生的空气洞弯转并终止于空气洞侧壁。最终获得位错密度低、表面原子级别平整的AlN薄膜。
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Figure CN118039455B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of group III nitride semiconductor fabrication technology, specifically relating to high crystal quality AlN thin films, their preparation methods and applications, and particularly to a low dislocation density AlN thin film with atomically flat heteroepitaxial surface, its preparation method and applications. Background Technology
[0002] High-quality AlN has wide applications in ultraviolet optoelectronic devices, electronic devices, and filters. Homoepitaxial growth on AlN substrates is the best choice for device applications. However, while homoepitaxial growth schemes using physical vapor transport (PVT) to prepare AlN substrates, or combining PVT with hydride vapor phase epitaxy (HVPE), can achieve the above goals well, they suffer from drawbacks such as high cost, difficulty in scaling up dimensions, and inability to achieve large-scale industrial production. These problems can be solved by preparing AlN thin films on heteroepitaxial growth on heteroepitaxial substrates.
[0003] However, due to the large lattice and thermal expansion coefficient mismatch between the most widely used (0001) plane AlN and the substrate, AlN films prepared by heteroepitaxial methods often have a high density of through-hole dislocations (10). 9 -10 10 cm -2 These defects, along with significant residual stress, are particularly problematic because these through-dislocations often extend into the active region of the device. These defects can act as nonradiative recombination centers or leakage channels, negatively impacting device performance such as efficiency, reliability, and lifetime. Therefore, epitaxially fabricating low-dislocation-density AlN films on heterogeneous substrates is crucial for achieving high-performance devices.
[0004] Currently, the main technical routes for preparing AlN thin films with (0001) surfaces on heterogeneous substrates are as follows:
[0005] One approach is to adjust the process parameters for low-temperature AlN nucleation and high-temperature AlN epitaxy to reduce the AlN dislocation density.
[0006] Secondly, an alternating growth mode AlN growth method is used on a flat heterogeneous substrate (such as alternating between low temperature and high temperature multiple times);
[0007] Third, the method of using pulsed group III metal sources or group V sources;
[0008] Fourth, an AlN lateral epitaxy method based on patterned substrates is adopted;
[0009] Fifth, the method of epitaxial growth on a heterogeneous substrate or high-temperature annealing after sputtering AlN is adopted.
[0010] While the methods described above have improved the crystal quality of AlN films to some extent, further development of more effective and stable approaches is needed to achieve atomically flat AlN films with low dislocation densities for realizing high-performance devices. Among these, lateral epitaxy using patterned substrates shows significant effectiveness and high stability in improving AlN crystal quality and has great potential for further development.
[0011] However, because AlN has a P63mc crystal structure, it differs greatly from commonly used substrates (such as sapphire). (crystal structure), which means that during the epitaxial growth of AlN directly through a patterned substrate, there is a transformation from the symmetry of the substrate lattice to the six-fold symmetry of AlN. The resulting atomic misalignment will further lead to dislocations during the closure process, fundamentally limiting the space for improving crystal quality. Summary of the Invention
[0012] The technical problem to be solved by this invention is how to overcome the dislocation multiplication during the polymerization process caused by the difference in crystal symmetry between AlN and the substrate in lateral epitaxy, so as to prepare AlN thin films with low dislocation density and atomic-level flatness.
[0013] To address the aforementioned technical problems, this invention proposes for the first time the specific patterning preparation of AlN / substrate templates on the (0001) plane. By growing AlN on a template with a specific patterned array of holes, the consistency of the lattice symmetry between the AlN epitaxial layer and the template plane is ensured. Furthermore, controllable lateral epitaxy of AlN is performed on the template, realizing a controllable polymerization process on a specific crystal plane. This greatly reduces crystal pillar distortion and dislocation multiplication, thereby achieving AlN thin films with low dislocation density and atomically flat surfaces.
[0014] In a first aspect, the present invention provides an AlN thin film having the following characteristics:
[0015] (1) Surface flatness reaches below 0.1 nm;
[0016] (2) Dislocation density is less than 1.0 × 10 8 cm -2 .
[0017] Secondly, the present invention provides a method for preparing an AlN thin film, comprising the following steps:
[0018] S1: An AlN layer with a (0001) facet is prepared on the substrate to form an AlN / substrate template;
[0019] S2: Fabricate a patterned array of holes on the AlN / substrate template;
[0020] S3: The polymerization process of AlN is controlled on the AlN / substrate template having the patterned array of holes to epitaxially obtain the AlN thin film.
[0021] In step S1, an AlN layer is prepared on the substrate using methods such as 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, and Si, etc.
[0022] The thickness of the AlN layer in the AlN / substrate template does not exceed 2000 nm, and is preferably in the range of 150-1500 nm.
[0023] In step S2, controlling the shape of the holes in the patterned AlN / substrate template is one of the core aspects of this solution. Through optimization of the etching process, the holes need to be strictly controlled to conform to the AlN pattern. or Crystal facets, with facet angles of 120 degrees (e.g.) Figure 1 The hole shape shown provides a basis for controllable crystal plane growth in the subsequent epitaxial process.
[0024] The periodic arrangement of the patterned array holes is a polygonal array, including any regular periodic arrangement such as parallelograms, rectangles, squares, hexagons, and rhombuses. Some patterned arrays, such as... Figure 2 As shown.
[0025] This invention reveals that the depth of the patterned array of holes is one of the important parameters for ensuring the smoothness of the AlN film surface. During further AlN epitaxy, polycrystalline or amorphous AlN is typically deposited at the bottom of the holes; if the hole depth is too shallow, the AlN deposited within the holes will disrupt the overall growth pattern, making it difficult for the AlN film to form an atomically smooth surface morphology. Therefore, the depth of the patterned array of holes is preferably 150-500 nm, and more preferably 200-350 nm.
[0026] This invention reveals that matching a suitable periodicity and size of the patterned array of holes is one of the key technologies for reducing dislocation density in AlN thin films. Experimental verification shows that the center-to-center distance (period) between any two adjacent patterned array holes is preferably 600-2000 nm, and more preferably 900-1500 nm. The size of the patterned array of holes is preferably 300-1400 nm, and more preferably 600-900 nm.
[0027] By controlling the above, the edge distance (hole period minus hole size) between any two adjacent patterned array holes is made within the range of 300-600 nm, preferably within the range of 300-450 nm. This ensures that during the lateral epitaxy of AlN on the patterned AlN / substrate template, mismatched dislocations located in the non-hole region and originating from the AlN / substrate interface are subjected to mirror forces, bend towards the air hole generated by the closing, and terminate at the sidewall of the air hole, thereby effectively reducing the dislocation density in the AlN film obtained in step S3.
[0028] The method for preparing the patterned array of holes is as follows: a patterned mask is formed on the AlN / substrate template by means of nanoimprinting or photolithography, and then the template is etched or corroded to form the patterned array of holes.
[0029] In step S3, controlling the AlN polymerization process on the patterned AlN / substrate template is the second core element of this patent. Specific growth temperatures, growth rates, and V / III ratios, among other epitaxial conditions, need to be selected to ensure that AlN can be maintained during further lateral epitaxy. or The crystal plane family completes the polymerization process without generating other growth crystal planes, thereby effectively suppressing the crystal pillar distortion caused by atomic misalignment during the closure process and reducing dislocation proliferation.
[0030] Preferably, in the polymerization process of AlN, the growth temperature is 1150-1400℃, more preferably 1200-1300℃; and the growth pressure is 20-200mbar, more preferably 40-100mbar.
[0031] In the MOCVD epitaxial growth of AlN thin films on patterned AlN / substrate templates as described in this invention, the molar flow ratio (V / III ratio) of ammonia (NH3) to Al source (trimethylaluminum, TMAl) is one of the key technologies for reducing the dislocation density in AlN thin films. Preferably, the V / III ratio is 200-1500; more preferably, the V / III ratio is 300-800.
[0032] Experimental results show that by optimizing the V / III ratio, the lateral epitaxial growth rate of AlN in S3 can be adjusted, allowing mismatched dislocations originating from the AlN / substrate interface in the non-void region to bend more fully towards air holes. More importantly, by optimizing the V / III ratio, the patterned holes can be scaled down proportionally without deformation during the lateral growth of AlN (S3). This indicates that the orientation of the laterally grown AlN crystal pillars is effectively controlled and unified, avoiding pillar twisting and tilting, suppressing dislocation generation during subsequent pillar closure, and thus reducing the dislocation density in the resulting AlN film.
[0033] Thirdly, the present invention provides an optoelectronic device or electronic device or filter, including the AlN thin film.
[0034] The beneficial effects achieved by this invention are as follows:
[0035] This invention has discovered that by performing a specific patterning process on an AlN / substrate template with a (0001) surface, the edges of the resulting hexagonal holes correspond to the AlN of the AlN substrate. or In the subsequent controllable crystal plane polymerization process of AlN epitaxial growth, the orientation of the crystal pillars is effectively controlled and unified, avoiding twisting and tilting of the pillars, and thus suppressing the generation of dislocations during the pillar closure process. Simultaneously, by matching the period and size of the pores, mismatched dislocations originating from the AlN / substrate interface in the non-pore region are bent towards the air holes generated during closure and terminated on the sidewalls of the air holes. Ultimately, an AlN thin film with low dislocation density and atomically smooth surface is obtained. Attached Figure Description
[0036] Figure 1 The periodic arrangement of partially patterned hole arrays includes (a) parallelogram arrays; (b) square arrays; (c) rectangular arrays; and (d) hexagonal arrays.
[0037] Figure 2 This is a flowchart of the AlN thin film preparation method described in Example 1. Detailed Implementation
[0038] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.
[0039] This invention specifically provides a method for preparing AlN thin films, such as... Figure 2 As shown, the core idea of AlN thin film preparation mainly involves three important steps:
[0040] S1: An AlN layer with a (0001) facet is prepared on the substrate to form an AlN / substrate template;
[0041] S2: Fabrication of a specific patterned array of holes on an AlN / substrate template;
[0042] S3: The polymerization process of AlN is controlled on an AlN / substrate template with patterned array holes to achieve the epitaxial preparation of AlN thin films.
[0043] The substrate mentioned in step S1 includes sapphire, SiC, and Si, etc.
[0044] Step S1 can be achieved using methods such as MOCVD, MBE, HVPE, or PVD (physical vapor deposition). A single method or a combination of multiple methods can be used, with MOCVD or PVD being preferred.
[0045] The process conditions for preparing the AlN / substrate template using the MOCVD method are as follows:
[0046] The first step is to place the substrate into the MOCVD reaction chamber and control the temperature of the reaction chamber at 800-1050℃, preferably 930-980℃. NH3 and TMAl are introduced into the reaction chamber to grow a low-temperature AlN nucleation layer on the substrate with a thickness of 10-30nm.
[0047] The second step is to maintain the NH3 flow and pause the TMA1 flow.
[0048] The third step involves raising the temperature of the reaction chamber to 1150-1400℃, preferably 1200-1300℃, and introducing TMAl into the reaction chamber to grow an AlN layer on the AlN nucleation layer. The thickness of the AlN layer does not exceed 2000nm, preferably 250-500nm.
[0049] The process conditions for preparing the AlN / substrate template using the PVD method are as follows:
[0050] The substrate is placed in the PVD reaction chamber, and the temperature of the reaction chamber is controlled in the range of 300-900℃, more preferably 500-800℃. Ar gas is introduced to bombard the Al target, and N2 is introduced to react with it, thereby sputtering and depositing AlN on the substrate. The sputtering power is 1000-6000W, more preferably 2500-4000W. The thickness of the sputtered AlN layer is no more than 2000nm, preferably 250-500nm.
[0051] Step S2 can be performed by forming a patterned mask on the AlN / substrate template using methods such as nanoimprinting or photolithography, followed by etching or etching to form patterned holes. The periodic arrangement of the holes is a polygonal array, including any regular periodic arrangement such as parallelograms, rectangles, squares, hexagons, and rhombuses.
[0052] in:
[0053] The shape of the holes is strictly controlled to be AlN or Crystalline family.
[0054] The aperture period is 600-2000nm, preferably 900-1500nm.
[0055] The aperture size is 300-1400nm, preferably 600-900nm.
[0056] The hole depth is 150-500nm, preferably 200-350nm.
[0057] Step S3 uses the MOCVD method to achieve epitaxial growth of AlN thin films on patterned AlN / substrate templates.
[0058] in:
[0059] The growth temperature is 1150-1400℃, preferably 1200-1300℃;
[0060] Growth pressure: 20-200 mbar, preferably 40-100 mbar;
[0061] The V / III ratio is 200-1500, preferably 300-800.
[0062] Example 1
[0063] This embodiment provides a method for preparing AlN thin films, specifically including the following steps:
[0064] Sl: A c-plane sapphire substrate was placed in the reaction chamber of an MOCVD equipment (3×2" Aixtron CCS FP-MOCVD). Under an H2 atmosphere, the growth temperature was raised to 950℃, and TMAl and NH3 were introduced to grow a 15nm thick AlN nucleation layer. Then, the NH3 was introduced while the TMAl introduction was stopped. The temperature was raised to 1230℃, and TMAl was introduced to grow a 250nm thick AlN film. Then, the NH3 and TMAl introduction were stopped, and the temperature was lowered to obtain an AlN / sapphire template with the (0001) plane.
[0065] S2: Patterned pores were fabricated on the AlN / sapphire template obtained in S1 using nanoimprinting and etching processes. The nanoimprint template had a period of 1000 nm, and the pores were hexagonal in shape with a diameter of 700 nm.
[0066] After etching, patterned holes with a periodic arrangement of regular hexagons (period 1000nm) are obtained on the AlN / sapphire template. The holes are circular in shape, with a diameter of 700nm and a depth of 200nm.
[0067] S3: Place a patterned AlN / sapphire template in the reaction chamber of an MOCVD system (3×2" Aixtron CCS FP-MOCVD). Under an H2 atmosphere, control the reaction chamber pressure at 50 mbar, raise the growth temperature to 1230℃, introduce NH3 and TMAl, maintain a V / III ratio of 600, and pass AlN through the substrate. After the crystal plane group polymerization, an AlN thin film with a thickness of 3000 nm was epitaxially grown.
[0068] Example 2
[0069] This embodiment provides a method for preparing AlN thin films, specifically including the following steps:
[0070] Sl: Place a c-plane sapphire substrate in the reaction chamber of a PVD equipment (Naura iTops A230 AlN Sputter System), raise the growth temperature to 650°C, introduce Ar gas and N2 at flow rates of 30 sccm and 180 sccm respectively, and sputter power of 3000W to sputter and deposit an AlN layer with a thickness of 500 nm on the (0001) plane of the sapphire substrate.
[0071] S2: Patterned holes were fabricated on the AlN / sapphire template obtained in S1 using photolithography and etching processes. The resulting pattern after photolithography consisted of periodically arranged square holes with a designed period of 1400 nm. The holes were hexagonal in shape with a side length of 700 nm. After etching, patterned holes with a periodic arrangement of squares (1400 nm period) were obtained on the AlN / sapphire template. The holes were hexagonal in shape with a side length of 700 nm and a depth of 300 nm.
[0072] S3: Place a patterned AlN / sapphire template in the reaction chamber of an MOCVD system (3×2" Aixtron CCS FP-MOCVD). Under an H2 atmosphere, control the reaction chamber pressure at 50 mbar, raise the growth temperature to 1230℃, introduce NH3 and TMAl, maintain a V / III ratio of 500, and pass AlN through the substrate. After the crystal planes are polymerized, an AlN thin film with a thickness of 3000 nm is epitaxially grown.
[0073] Comparative Example 1
[0074] This comparative example provides a method for preparing an AlN epitaxial thin film, which directly uses a sapphire substrate as a template and has circular holes. The method specifically includes the following steps:
[0075] S1: Use the c-plane sapphire substrate directly as a template and clean it thoroughly;
[0076] S2: Patterned holes are fabricated on a sapphire substrate using nanoimprinting and etching processes. The mask obtained by nanoimprinting consists of periodically arranged regular hexagonal holes with a designed period of 1000 nm. The holes are circular with a diameter of 700 nm.
[0077] After etching, patterned holes with a periodic arrangement of regular hexagons (period 1000nm) are obtained on the sapphire template. The holes are circular in shape, with a diameter of 700nm and a depth of 200nm.
[0078] S3: Place a patterned AlN / sapphire template in the reaction chamber of the MOCVD equipment (3×2" Aixtron CCS FP-MOCVD), control the pressure of the reaction chamber to 50mbar under H2 atmosphere, raise the growth temperature to 1230℃, introduce NH3 and TMAl, maintain the V / III ratio at 600, and epitaxially grow an AlN film with a thickness of 3000nm.
[0079] Effect verification
[0080] The AlN films obtained in Example 1, Example 2, and Comparative Example 1 were tested using commonly used testing methods in the art:
[0081] (1) Atomic force microscopy detection: 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);
[0082] (2) Detection by plane transmission electron microscopy:
[0083] The dislocation density of the AlN thin film obtained in Example 1 is 4.2 × 10⁻⁶. 7 cm -2 ;
[0084] The dislocation density of the AlN thin film obtained in Example 2 is 4.9 × 10⁻⁶. 7 cm -2 ;
[0085] The dislocation density of the AlN thin film obtained in Comparative Example 1 is 6.5 × 10⁻⁶. 8 cm -2 ;
[0086] The test results above show that Example 1 and Example 2 have significantly lower dislocation densities compared to Comparative Example 1.
[0087] Comparative Example 2
[0088] The difference from Example 1 is that step S2 is omitted, and the AlN polymerization process is directly controlled on the AlN / substrate template to obtain the AlN thin film epitaxially.
[0089] The results show that, due to omitting step S2, the surface smoothness of the obtained AlN film is 0.21 nm (3 μm × 3 μm); the dislocation density of the obtained AlN film is 2.3 × 10⁻⁶. 9 cm -2 .
[0090] Comparative Example 3
[0091] The difference from Embodiment 1 is that in step S2, the shape of the patterned array holes is circular.
[0092] The results show that due to the unsuitable shape design of the patterned array holes, a multifaceted competition occurred during the subsequent epitaxial process due to the transformation from triplet symmetry to sixfold symmetry. The resulting AlN film had a surface flatness of 0.17 nm (3 μm × 3 μm) and a dislocation density of 3.2 × 10⁻⁶. 8 cm -2 .
[0093] Comparative Example 4
[0094] The difference from Example 1 is that in step S2, the depth of the patterned array holes is 80nm.
[0095] The results show that due to the shallow depth of the pores, it is difficult to form sufficiently large pores on the outer sides of the obtained AlN film, resulting in poor dislocation suppression. The surface smoothness of the obtained AlN film is 0.25 nm (3 μm × 3 μm), and the dislocation density is 1.2 × 10⁻⁶. 9 cm -2 .
[0096] Comparative Example 5
[0097] The difference from Example 1 is that the period of any two adjacent patterned array holes is 500nm and the size of the holes is 250nm.
[0098] The results show that, due to the mismatch between the periodic arrangement of the pores and their sizes, the dislocation density in the obtained AlN film is 7.0 × 10⁻⁶. 8 cm -2 .
[0099] Comparative Example 6
[0100] The difference from Example 1 is that the growth temperature in the polymerization process of AlN is 1200℃, the growth pressure is 50mbar, and the V / III ratio is 50.
[0101] The results show that, due to unsuitable matching of epitaxial preparation conditions, it is impossible to maintain a single AlN. In the case of crystal plane family polymerization, the dislocation density in the resulting AlN film is 2.1 × 10⁻⁶. 8 cm -2 .
[0102] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.
Claims
1. A method for preparing an AlN thin film, comprising the following steps: S1: An AlN layer with a (0001) facet is prepared on the substrate to form an AlN / substrate template; S2: Fabricate a patterned array of holes on the AlN / substrate template; S3: The polymerization process of AlN is controlled on the AlN / substrate template having the patterned array of holes to epitaxially obtain the AlN thin film; In step S2, the patterned array of holes has the following characteristics: The edges of the obtained hexagonal holes correspond to AlN or Crystalline family; The angle between the faces is 120 degrees. In step S3, the polymerization process of AlN consists only of AlN or The crystal plane family is completed without generating any other growth crystal planes; The AlN thin film has the following characteristics: (1) Surface flatness reaches below 0.1 nm; (2) Dislocation density is less than 1.0 × 10 8 cm -2 .
2. The method for preparing AlN thin films according to claim 1, characterized in that: In step S2, the periodic arrangement of the patterned array holes is a polygon array.
3. The method for preparing AlN thin films according to claim 1, characterized in that: In step S2, the depth of the patterned array holes is 150-500 nm.
4. The method for preparing AlN thin films according to claim 1, characterized in that: In step S2, the edge distance between any two adjacent patterned array holes is 300-600 nm.
5. The method for preparing AlN thin films according to claim 1, 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 apertures is 300-1400 nm.
6. The method for preparing AlN thin films according to claim 1, characterized in that: In step S3, during the polymerization process control of AlN, the growth temperature is 1150-1400℃, the growth pressure is 20-200mbar, and the molar flow ratio of ammonia to Al source is 200-1500.
7. The AlN thin film obtained by the preparation method according to any one of claims 1-6.
8. An optoelectronic device comprising the AlN thin film of claim 7.