AlN epitaxial structure and semiconductor device
By controlling the thickness and growth conditions of the AlN base layer, a regular hexagonal pore structure was formed. Combined with the two-stage merging layer growth process, the problem of grain boundary alignment in the AlN epitaxial layer was solved, and high-quality AlN material growth was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-28
- Publication Date
- 2026-03-03
AI Technical Summary
Existing technologies have resulted in improper placement and shape of pore structures in AlN epitaxial layers, leading to difficulties in grain boundary alignment, high dislocation density, and negatively impacting the quality of AlN materials.
By controlling the thickness of the AlN base layer and growth conditions, a regular hexagonal pore structure is formed. Combined with a two-stage merging layer growth process, the dislocation density is reduced.
It significantly improved the quality of AlN epitaxial layers, reduced dislocation density, and enhanced crystal flatness and luminescence efficiency.
Smart Images
Figure CN223963602U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of nitride semiconductor device technology, and in particular to an AlN epitaxial structure and semiconductor device. Background Technology
[0002] AlN single crystal materials have a large bandgap (6.2 eV) and a direct bandgap band structure, making them ideal for deep ultraviolet optoelectronic devices such as light-emitting diodes, lasers, and detectors. Furthermore, AlN single crystal materials possess excellent properties such as high breakdown voltage and low dielectric constant, making them valuable for applications in power electronics. The growth of UVC LEDs requires a high-quality AlN epitaxial layer as a foundation, which plays a crucial role in improving luminous efficiency and reducing non-radiative recombination.
[0003] Some existing technologies introduce a porous structure into the AlN epitaxial layer by adjusting the process conditions during the epitaxial growth of the AlN epitaxial layer to form a void-forming layer and a void-closing layer. This reduces dislocation density and inhibits crack propagation, thereby providing a high-quality AlN epitaxial layer.
[0004] However, existing technologies generally place the openings at the interface between the substrate and AlN, or at a distance of less than 500 nm between AlN and the substrate. These openings are usually irregular, which makes it difficult to align the grain boundaries when the hole structures are merged, and new dislocations are easily generated during the merging process.
[0005] Specifically, regarding the shape of the pores, the inventors of this invention discovered that if suitable AlN pore opening conditions are adopted, making the AlN pores regular and uniform hexagonal or other shapes, the dislocation density can be effectively reduced during AlN merging, thereby achieving higher quality AlN materials. Regarding the location of the pores, the inventors discovered that when the pore structure in the AlN layer is thin, such as in the range of 100-200 nm, the initial AlN dislocation density is high, resulting in a high pore density. The tensile stress generated during pore merging is large, which can easily lead to longer edge cracks. If the AlN pore thickness is thick, such as exceeding 0.8-1 μm, the pore density decreases, which reduces the effect of dislocation annihilation by image force during merging, ultimately leading to deviations in the quality of the AlN crystal. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide an AlN epitaxial structure and a semiconductor device. To achieve the aforementioned objective, the technical solution adopted by this invention includes:
[0007] In a first aspect, the present invention provides an AlN epitaxial structure, which includes an AlN base layer, an AlN forming layer and an AlN merging layer stacked sequentially along a specified direction;
[0008] The AlN base layer is a dense layer with a thickness of 600-750 nm; the AlN forming layer and the AlN merging layer have multiple embedded pore structures, and along the specified direction, any one of the pore structures opens in the AlN forming layer and closes in the AlN merging layer;
[0009] Furthermore, when viewed from the interface between the AlN forming layer and the AlN merging layer, the proportion of pores with selected cross-sectional shapes in all the pore structures is more than 50%.
[0010] Secondly, this utility model also provides a semiconductor device, including the above-mentioned AlN epitaxial structure and a functional structure constructed based on the AlN epitaxial structure.
[0011] Based on the above technical solution, compared with the prior art, the beneficial effects of this utility model include at least the following:
[0012] The epitaxial structure provided by this invention reduces the chance of irregular void formation by appropriately controlling the thickness of the AlN base layer, adjusts the density of void formation, and guides the void structure towards a uniform cross-sectional shape, thereby preventing the void structure from forming irregular and inconsistent cross-sectional shapes, avoiding alignment difficulties when merging void structures, reducing the generation of new dislocations, and significantly improving the quality of the AlN epitaxial layer.
[0013] The above description is only an overview of the technical solution of this utility model. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of this utility model are described below with reference to the accompanying drawings. Attached Figure Description
[0014] Figure 1a This is a schematic diagram of the AlN opening cross-sectional shape provided in the background art of this utility model;
[0015] Figure 1b This is a schematic diagram of the AlN opening cross-sectional shape provided in a typical embodiment of this utility model;
[0016] Figure 2 This is a schematic diagram of the growth process of an AlN epitaxial structure provided in a typical embodiment of this utility model;
[0017] Figure 3 This is a schematic diagram of the AlN epitaxial structure provided in a typical embodiment of this utility model;
[0018] Figure 4This is a schematic diagram of the AlN epitaxial structure provided in another typical embodiment of this utility model.
[0019] Explanation of reference numerals in the attached figures:
[0020] 100, Substrate; 110, AlN base layer; 120, AlN forming layer; 130, AlN merging layer;
[0021] 200, Substrate; 210, AlN base layer; 220, AlN forming layer; 230, First merged sublayer; 240, Second merged sublayer. Detailed Implementation
[0022] In view of the shortcomings of the prior art, the inventor of this case, through long-term research and extensive practice, has come up with the technical solution of this utility model. The following will further explain the technical solution, its implementation process, and its principles.
[0023] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.
[0024] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component or method step from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components or method steps.
[0025] This utility model embodiment provides an AlN epitaxial structure, which includes an AlN base layer, an AlN forming layer, and an AlN merging layer stacked sequentially along a specified direction; the AlN base layer is a dense layer with a thickness of 600-750 nm; the AlN forming layer and the AlN merging layer have embedded multiple pore structures, and along the specified direction, any one of the pore structures opens into the AlN forming layer and closes into the AlN merging layer; and if viewed from the interface of the AlN forming layer and the AlN merging layer, the proportion of pores with a selected cross-sectional shape in all the pore structures is more than 50%.
[0026] Regarding specific details, in some embodiments, the pore density of the pore structure in the AlN merging layer is 1×10⁻⁶. 9 -2×10 11 cm -2 Regarding the definition of pore density, those skilled in the art will understand that pore density refers to the number of pore structures that can be observed within a certain cross-sectional area.
[0027] In some implementations, the selected cross-sectional shape is a hexagonal structure.
[0028] See Figure 1a and Figure 1b In contrast, conventional existing technologies that use porous structures to alleviate stress and eliminate dislocations and cracks typically place the openings (the height from the beginning of the porous structure to the substrate) at the interface between the substrate and the buffer layer, or within 500 nm of the buffer layer. Therefore, the initial dislocation density is high, and the holes are generally irregular or non-uniform (e.g., forming various different shape combinations). This makes it difficult to align the grain boundaries during merging of air holes, and new dislocations are easily generated during merging, leading to a series of problems. In contrast, this invention uses suitable AlN opening conditions and locations, resulting in regular and uniform AlN holes (preferably hexagonal). This makes it easier to align the grain boundaries during AlN merging, effectively reducing the dislocation density and achieving high-quality epitaxial growth of AlN materials.
[0029] Regarding the characteristics of the pore structure, in some embodiments, the pore structure includes a continuous first part and a second part, with the cross-sectional area of the first part gradually increasing and the cross-sectional area of the second part gradually decreasing along the specified direction; with the specified direction as the height direction, the thickness of the AlN forming layer is 150-300 nm.
[0030] In some implementations, the hole structure is completely closed at the end of the second portion along the specified direction.
[0031] In some more preferred embodiments, the end of the second part is open, and the hole structure further includes a third part connected to the second part, the hole structure being completely closed at the end of the third part; and along the specified direction, the cross-sectional area of the second part has a first gradient of change, the cross-sectional area of the third part has a second gradient of change, and the absolute value of the first gradient of change is greater than the absolute value of the second gradient of change.
[0032] In some specific implementations, the specified direction is used as the height direction, and the height of the third part is greater than the height of the second part.
[0033] In some embodiments, the AlN epitaxial structure further includes a substrate and an AlN underlayer, wherein the AlN underlayer is formed on the surface of the substrate, and the AlN base layer is formed on the surface of the AlN underlayer. Of course, if the AlN epitaxial structure is peeled off from the substrate using a stripping technique and used as a new growth substrate, the substrate is not included, but it still falls within the protection scope of this invention.
[0034] Correspondingly, a second aspect of this utility model embodiment also provides a method for preparing an AlN epitaxial structure, which includes the following steps:
[0035] A dense AlN base layer is epitaxially grown, and the growth thickness of the AlN base layer is controlled to be 600-750 nm.
[0036] An AlN forming layer is formed under the first process conditions, such that the AlN forming layer forms a plurality of open pores; the proportion of openings with a selected opening cross-sectional shape on the surface of the AlN forming layer in all open pores is more than 50%.
[0037] In the second process, an AlN merging layer is grown, causing the open pores to gradually close as the AlN merging layer thickens, forming a closed pore structure.
[0038] The selected opening cross-sectional shape of the AlN epitaxial structure is hexagonal, and the first process conditions include: growth pressure of 100-200 Torr, V / III ratio of 6000-10000, growth temperature of 800-850℃, and growth rate controlled at 0.15-0.3 μm / h.
[0039] The aforementioned process conditions, especially the precise control of the growth rate within a certain range, are key factors in forming a uniform hexagonal cross-sectional shape.
[0040] The second process conditions for AlN epitaxial structures include: growth pressure of 50-100 Torr, V / III ratio of 10-1000, and growth temperature of 1100-1300℃.
[0041] The epitaxial growth of the AlN merging layer in the AlN epitaxial structure is divided into a first growth stage and a second growth stage; the V / III ratio of the first growth stage is lower than that of the second growth stage, and the growth temperature of the first growth stage is higher than that of the second growth stage.
[0042] The first growth stage of the AlN epitaxial structure has a V / III ratio of 10-100 and a growth temperature of 1200-1300℃; the second growth stage has a V / III ratio of 500-1000 and a growth temperature of 1100-1150℃.
[0043] As a specific example, the formation process of AlN epitaxial structures can be found in [reference needed]. Figure 2As shown, AlN growth is generally performed on a heterogeneous substrate 100 with mismatched lattice constants. This results in a high density of dislocations at the substrate-AlN interface during the AlN nucleation stage due to lattice mismatch. If holes are directly opened at this time, or if the AlN thickness is thin, the hole density will be high and the hole shape will be irregular. Therefore, it is necessary to grow an AlN base layer 110 of a certain thickness to reduce the dislocation density before opening holes. Through the inventor's experimental research, the optimal range of this thickness is 600-750nm. If the AlN base layer 110, i.e., the film layer marked as HTALN1 in the figure, is relatively thin, for example, within 100-200 nm, the initial high AlN dislocation density will lead to a high pore density. The tensile stress generated during pore coalescence will be large, which can easily lead to longer edge cracks. If the HTALN1 layer is too thick, for example, exceeding 0.8-1 μm, it will result in a low dislocation density and a reduced number of pores, thus reducing the number of dislocations that will eventually annihilate. This is detrimental to the final reduction of dislocation density. After multiple adjustments, the optimal pore density is 1 × 10⁻⁶. 19 -2×10 20 / cm 2 about.
[0044] After preparing a suitable thickness of HTALN1, hexagonal pores can be opened at the corresponding dislocation sites by using appropriate AlN growth conditions. The optimal growth conditions are a pressure of 100-200 Torr, a V / III ratio of 6000-10000, a growth temperature of 800-850℃, and a growth rate controlled at 0.15-0.3 μm / h. Under these opening conditions, hexagonal pores are more likely to be formed, rather than randomly forming circular, rhomboid, or irregularly shaped pores. This is crucial for subsequent pore merging. The optimal thickness of the AlN forming layer 120, represented in the figure as a thin RnAlN layer, is 150-300 nm. If the thickness is too thin, the pore opening is smaller, reducing the lateral area that blocks dislocations and hindering the reduction of dislocation density. If the thickness is too thick, the pores tend to connect, forming irregular pores, which leads to the generation of new dislocations during subsequent pore merging, also hindering the reduction of dislocation density.
[0045] The AlN merging layer 130, namely the film layer represented by HTALN2 in the figure, mainly functions to merge the open pores of RnAlN, reduce the dislocation density by utilizing dislocation annihilation at the growth interface, and at the same time, it is necessary to obtain a smooth, crack-free and pore-free AlN surface. The HTALN2 layer can grow and merge under one condition until complete merging, or it can be divided into HTALN2-1 sublayer and HTALN2-2 sublayer. The HTALN2-1 sublayer is used to quickly shrink the hexagonal pores but not to completely merge them. The HTALN2-2 sublayer slows down the merging rate based on the HTALN2-1 sublayer, because merging too quickly can easily generate tensile stress, which can lead to cracks in AlN. Therefore, the optimal V / III ratio for the HTALN2-1 sublayer is 10-100, and the optimal V / III ratio for the HTALN2-2 sublayer is 500-1000. The optimal growth conditions for the HTALN2 sublayer are a pressure of 50-100 Torr and a growth temperature of 1200-1300℃. The growth temperature of the HTALN2-2 sublayer can be lower than that of the HTALN2-1 sublayer.
[0046] However, it should be noted that although the two stages with different merging speeds are referred to as two "sublayers" in this utility model, in the actual epitaxial structure, it is difficult to have a clear dividing line between sublayers. The characteristics of different sublayers are mainly reflected by the different merging slopes of the pore structure in the layer.
[0047] A third aspect of this utility model embodiment also provides a semiconductor device, which includes the AlN epitaxial structure provided in any of the above embodiments and a functional structure constructed based on the AlN epitaxial structure.
[0048] The functional structure of the AlN epitaxial structure includes a first conductive semiconductor material layer, an active layer, and a second conductive semiconductor material layer stacked sequentially, wherein the first conductive semiconductor material layer and the second conductive semiconductor material layer have opposite conductivity characteristics.
[0049] The technical solution of this utility model is further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only used to illustrate this utility model and do not limit the scope of this utility model.
[0050] Example 1
[0051] This embodiment illustrates the fabrication process of an AlN epitaxial structure, which is described in [reference needed]. Figure 3 As shown, the specific process includes:
[0052] S1: Sputtered AlN bottom layer: A 15 nm AlN thin film is sputtered on a sapphire substrate 100 as the AlN bottom layer.
[0053] S2: Place the substrate 100 with the AlN bottom layer into the MOCVD equipment, raise the temperature to 1150℃, the pressure to 50 Torr, and simultaneously introduce H2 and NH3 to grow the AlN base layer 110 with a final thickness of 650 nm.
[0054] S3: Growth of AlN Cambium 120: The growth temperature was reduced to 850℃, the pressure was 100 Torr, the V / III ratio was increased to 8000, and the growth rate was 0.15 μm / h. A 300 nm AlN cambium 120 was grown under low temperature, slow speed and high V / III conditions.
[0055] S4: Growth of AlN merging layer 130: The growth temperature was increased to 1200℃, the pressure was 50 Torr, and the V / III ratio was reduced to 50. A 2000 nm AlN merging layer 130 was grown under high temperature and low V / III conditions to form pores inside the epitaxial structure.
[0056] Observing the AFM images of the surfaces of AlN forming layer 120 and AlN merging layer 130, it can be found that the hexagonal cavity structure makes a positive contribution to the epitaxial quality of AlN, giving it excellent properties such as high flatness and low dislocation density.
[0057] Example 2
[0058] This embodiment illustrates the fabrication process of an AlN epitaxial structure, which is described in [reference needed]. Figure 4 As shown, the specific process includes:
[0059] S1: Sputtered AlN bottom layer: A 15 nm AlN thin film is sputtered on a sapphire substrate 200 as the AlN bottom layer.
[0060] S2: Place the substrate 200 with the AlN bottom layer into the MOCVD, raise the temperature to 1150℃, the pressure to 50 Torr, and simultaneously introduce H2 and NH3 to grow the AlN base layer 210 with a final thickness of 650 nm.
[0061] S3: Growth of AlN Cambium 220: The growth temperature was reduced to 800℃, the pressure was 100 Torr, the V / III ratio was increased to 8000, and the growth rate was 0.15 um / h. A 300 nm AlN cambium 220 was grown under low temperature, slow speed and high V / III conditions.
[0062] S4: Growth of the first merged sublayer 230: The growth temperature is increased to 1200℃, the pressure is 50 Torr, and the V / III ratio is reduced to 50. The first merged sublayer 230 of 500 nm is grown under high temperature and low V / III conditions to form pores inside the material.
[0063] S5: Growth of the second merged sublayer 240: The growth temperature is increased to 1150℃, the pressure is 50 Torr, and the V / III ratio is increased to 500. The second merged sublayer 240 of 1500 nm is grown under high temperature and low V / III conditions to form pores inside the material.
[0064] This embodiment employs a two-stage merging method, which significantly reduces the tensile stress caused by rapid merging, resulting in higher flatness and lower dislocation density in the AlN epitaxial layer.
[0065] Based on the above embodiments and comparative examples, it is clear that the technical solution provided by this utility model reduces the chance of irregular pore formation by controlling the appropriate AlN base layer thickness, adjusts the generation density of pore structures, and guides the pore structures to tend towards the same cross-sectional shape by controlling the growth conditions of the AlN forming layer, thereby preventing the pore structures from forming irregular and inconsistent cross-sectional shapes, avoiding alignment difficulties when pore structures merge, reducing the generation of new dislocations, and significantly improving the quality of the AlN epitaxial layer.
[0066] It should be understood that the above embodiments are merely illustrative of the technical concept and features of this utility model, and are intended to enable those skilled in the art to understand the content of this utility model and implement it accordingly. They should not be construed as limiting the scope of protection of this utility model. All equivalent changes or modifications made in accordance with the spirit and essence of this utility model should be included within the scope of protection of this utility model.
Claims
1. An AlN epitaxial structure, characterized in that, It includes an AlN base layer, an AlN forming layer, and an AlN merging layer that are stacked sequentially along a specified direction; The AlN base layer is a dense layer with a thickness of 600-750 nm; the AlN forming layer and the AlN merging layer have multiple embedded pore structures, and along the specified direction, any one of the pore structures opens in the AlN forming layer and closes in the AlN merging layer; Furthermore, when viewed from the interface between the AlN forming layer and the AlN merging layer, the proportion of pores with selected cross-sectional shapes in all the pore structures is more than 50%.
2. The AlN epitaxial structure according to claim 1, characterized in that, The pore density of the pore structure in the AlN composite layer is 1×10⁻⁶. 9 -2×10 11 / cm 2 .
3. The AlN epitaxial structure according to claim 1, characterized in that, The selected cross-sectional shape is a hexagonal structure.
4. The AlN epitaxial structure according to claim 2, characterized in that, The hole structure includes a continuous first part and a second part. Along the specified direction, the cross-sectional area of the first part has a gradually increasing trend, and the cross-sectional area of the second part has a gradually decreasing trend. With the specified direction as the height direction, the thickness of the AlN forming layer is 150-300 nm.
5. The AlN epitaxial structure according to claim 4, characterized in that, Along the specified direction, the hole structure is completely closed at the end of the second part.
6. The AlN epitaxial structure according to claim 4, characterized in that, The second part is open at its end, and the hole structure also includes a third part connected to the second part. The hole structure is completely closed at the end of the third part. Along the specified direction, the cross-sectional area of the second part has a first gradient, and the cross-sectional area of the third part has a second gradient. The absolute value of the first gradient is greater than the absolute value of the second gradient.
7. The AlN epitaxial structure according to claim 6, characterized in that, Using the specified direction as the height direction, the height of the third part is greater than the height of the second part.
8. The AlN epitaxial structure according to claim 7, characterized in that, It also includes a substrate and an AlN underlayer, wherein the AlN underlayer is formed on the surface of the substrate and the AlN base layer is formed on the surface of the AlN underlayer.
9. A semiconductor device, characterized in that, It includes the AlN epitaxial structure as described in any one of claims 1-8 and the functional structure constructed based on the AlN epitaxial structure.
10. The semiconductor device according to claim 9, characterized in that, The functional structure includes a first conductive semiconductor material layer, an active layer, and a second conductive semiconductor material layer stacked sequentially, with the first and second conductive semiconductor material layers having opposite conductivity characteristics.