High-quality AlN thin film material and preparation method thereof

Abstract

The invention discloses a high-quality AlN thin film material and a preparation method thereof. The epitaxial structure comprises an AlN base layer, a forming layer and a merging layer, the base layer is a dense layer and has the thickness of 600-750 nm; a plurality of hole structures are embedded in the forming layer and the merging layer, are opened in the forming layer and are closed in the merging layer; and the ratio of the holes with the selected cross section shape is more than 50%. According to the technical scheme provided by the invention, the opportunity of forming irregular holes is reduced through proper thickness control of the AlN base layer, the generation density of the hole structure is adjusted, and the hole structure tends to be in a uniform cross section shape through control of the growth condition of the AlN forming layer, so that the irregular and non-uniform cross section shape of the hole structure is prevented from being formed; the alignment difficulty during the combination of the hole structures is avoided, the generation of newly added dislocation is reduced, and the quality of the AlN epitaxial layer is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nitride semiconductor devices, and in particular to a high-quality AlN thin film material and a preparation method thereof. Background Art

[0002] AlN single crystal material has a large bandgap width (6.2eV) and a direct bandgap energy band structure, so it is very suitable for deep ultraviolet optoelectronic devices, such as light-emitting diodes, lasers, detectors, etc. At the same time, AlN single crystal material also has excellent properties such as high breakdown voltage and small dielectric constant, which makes it have important application value in the field of power electronic devices. The growth of UVC LED requires a high-quality AlN epitaxial layer as a basis, which plays an important role in improving luminous efficiency and reducing non-radiative recombination.

[0003] Some existing technologies introduce a hole structure into the AlN epitaxial layer by adjusting process conditions to form a hole forming layer and a hole closing layer during epitaxial growth of the AlN epitaxial layer, thereby reducing dislocation density and inhibiting crack extension, thereby providing a high-quality AlN epitaxial layer.

[0004] However, the general existing technology generally opens holes at the interface between the substrate and AlN, or at a close distance between AlN and the substrate, such as holes formed within 500 nm, and the holes are usually irregular, which makes it difficult to align the grain boundaries when the hole structure merges, and new dislocations are easily generated when merging.

[0005] Specifically, regarding the shape of the holes, the inventors of the present invention have found that if appropriate AlN opening conditions are adopted so that the AlN holes are regular and uniform hexagonal or other shapes, the dislocation density of AlN can be effectively reduced when merging, thereby achieving higher quality AlN materials; and regarding the opening position, the inventors have found that when the hole structure in the AlN layer has a thin opening thickness, such as in the range of 100-200 nm, the initial AlN dislocation density is high, resulting in a high opening density, and the tensile stress generated when the holes are merged is large, which can easily lead to longer edge cracks. If the AlN opening thickness is thick, such as exceeding 0.8-1um, the opening density will decrease, resulting in a poor effect of using image force to annihilate dislocations when merging, ultimately leading to AlN crystal quality deviation. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a high-quality AlN thin film material and a preparation method thereof. To achieve the above-mentioned invention objectives, the technical solutions adopted by the present invention include: In a first aspect, the present invention provides an AlN epitaxial structure, which includes an AlN base layer, an AlN formation layer, and an AlN merging layer stacked in sequence along a specified direction; The AlN base layer is a dense layer with a thickness of 600-750 nm; a plurality of hole structures are embedded in the AlN formation layer and the AlN merged layer, and along the specified direction, any of the hole structures opens in the AlN formation layer and closes in the AlN merged layer; Furthermore, if observed from the interface between the AlN forming layer and the AlN merging layer, the proportion of holes having the selected cross-sectional shape in all the hole structures is greater than 50%.

[0007] In a second aspect, the present invention further provides a method for preparing an AlN epitaxial structure, comprising: Epitaxially growing a dense AlN base layer, and controlling the growth thickness of the AlN base layer to be 600-750 nm; An AlN formation layer is formed under a first process condition, so that the AlN formation layer forms a plurality of open holes; the openings having the selected opening cross-sectional shape on the surface of the AlN formation layer account for more than 50% of all the open holes; The AlN merged layer is grown under the second process, so that the open holes are gradually closed as the AlN merged layer gradually thickens, forming a closed hole structure.

[0008] In a third aspect, the present invention further provides a semiconductor device, comprising the above-mentioned AlN epitaxial structure and a functional structure constructed based on the AlN epitaxial structure.

[0009] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention at least include: The technical solution provided by the present invention reduces the chance of irregular hole formation by appropriately controlling the thickness of the AlN base layer, adjusts the generation density of the hole structure, and guides the hole structure toward a uniform cross-sectional shape by controlling the growth conditions of the AlN formation layer, thereby preventing the hole structure from forming an irregular and non-uniform cross-sectional shape, avoiding alignment difficulties when the hole structure is merged, reducing the generation of new dislocations, and significantly improving the quality of the AlN epitaxial layer.

[0010] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement them according to the contents of the specification, the following is a description of the preferred embodiments of the present invention in conjunction with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1a It is a schematic diagram of the cross-sectional shape of an AlN opening provided by the background technology of the present invention; Figure 1b It is a schematic diagram of the cross-sectional shape of an AlN opening provided by a typical implementation case of the present invention; Figure 2 It is a schematic diagram of the growth process of an AlN epitaxial structure provided by a typical implementation case of the present invention; Figure 3 It is a structural schematic diagram of an AlN epitaxial structure provided by a typical implementation case of the present invention; Figure 4 This is a surface AFM photograph of an AlN formation layer provided in a typical embodiment of the present invention; Figure 5 This is a surface AFM photograph of an AlN epitaxial structure provided by a typical embodiment of the present invention; Figure 6 It is a structural schematic diagram of an AlN epitaxial structure provided by another typical implementation case of the present invention.

[0012] Description of reference numerals: 100, substrate; 110, AlN base layer; 120, AlN formation layer; 130, AlN merged layer; 200, substrate; 210, AlN base layer; 220, AlN formation layer; 230, first merged sublayer; 240, second merged sublayer. DETAILED DESCRIPTION

[0013] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0014] In the following description, many specific details are set forth to facilitate 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 protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0015] Moreover, relational terms such as “first” and “second” are merely used to distinguish one component or method step from another with the same name, but do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0016] An embodiment of the present invention provides an AlN epitaxial structure, which includes an AlN base layer, an AlN forming layer and an AlN merged layer stacked in sequence along a specified direction; the AlN base layer is a dense layer with a thickness of 600-750nm; a plurality of hole structures are embedded in the AlN forming layer and the AlN merged layer, and along the specified direction, any of the hole structures opens in the AlN forming layer and is closed in the AlN merged layer; and if observed from the interface between the AlN forming layer and the AlN merged layer, the proportion of holes with a selected cross-sectional shape in all the hole structures is more than 50%.

[0017] Regarding specific details, in some embodiments, the hole density of the hole structure in the AlN merged layer is 1×10 9 -2×10 11 cm -2 Regarding the definition of pore density, those skilled in the art can understand that pore density refers to the number of pore structures that can be observed within a certain cross-sectional area.

[0018] In some embodiments, the selected cross-sectional shape is a hexagonal structure.

[0019] See also Figure 1a and Figure 1b In contrast, the conventional existing technology uses a hole structure to relieve stress and eliminate dislocations and cracks. The general hole opening position (referring to the height from the beginning of the hole structure to the substrate) is opened at the interface between the substrate and the buffer layer, or the hole is opened within 500 nm of the buffer layer. Therefore, the initial dislocation density is high and the holes are generally irregular or non-uniform (for example, a variety of different shape combinations are formed), which makes it difficult to align the grain boundaries of the air holes when they merge, and new dislocations are easily generated when they merge, causing a series of problems. The present invention adopts appropriate AlN hole opening conditions and positions to make the AlN holes regular and uniform in shape (most preferably hexagonal), so that the AlN grain boundaries are easier to align when they merge, which can effectively reduce the dislocation density, thereby achieving the epitaxial growth of high-quality AlN materials.

[0020] Regarding the characteristics of the hole structure, in some embodiments, the hole structure includes a continuous first part and a second part, and along the specified direction, the cross-sectional area of ​​the first part has a tendency to gradually increase, and the cross-sectional area of ​​the second part has a tendency to gradually decrease; taking the specified direction as the height direction, the thickness of the AlN formation layer is 150-300nm.

[0021] In some embodiments, along the specified direction, the hole structure is completely closed at the end of the second portion.

[0022] Or in some more preferred embodiments, the end of the second part is in an open state, the hole structure also includes a third part connected to the second part, and the hole structure is 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 change gradient, the cross-sectional area of ​​the third part has a second change gradient, and the absolute value of the first change gradient is greater than the absolute value of the second change gradient.

[0023] Specifically in some embodiments, taking the designated direction as the height direction, the height of the third portion is greater than the height of the second portion.

[0024] In addition, in some embodiments, the AlN epitaxial structure further includes a substrate and an AlN bottom layer, wherein the AlN bottom layer is formed on the surface of the substrate, and the AlN base layer is formed on the surface of the AlN bottom layer. Of course, if the AlN epitaxial structure is peeled off from the substrate by peeling technology and used as a new growth substrate, the substrate is not included at this time, but it still falls within the protection scope of the present invention.

[0025] Correspondingly, the second aspect of the embodiment of the present invention further provides a method for preparing an AlN epitaxial structure, which comprises the following steps: Epitaxially growing a dense AlN base layer, and controlling the growth thickness of the AlN base layer to be 600-750 nm; An AlN formation layer is formed under a first process condition, so that the AlN formation layer forms a plurality of open holes; the openings having the selected opening cross-sectional shape on the surface of the AlN formation layer account for more than 50% of all the open holes; The AlN merged layer is grown under the second process, so that the open holes are gradually closed as the AlN merged layer gradually thickens, forming a closed hole structure.

[0026] The selected opening cross-sectional shape of the AlN epitaxial structure is a hexagon, and the first process conditions include: growth pressure of 100-200 Torr, V / III ratio of 6000-10000, growth temperature of 800-850° C., and growth rate controlled at 0.15-0.3 um / h.

[0027] The above 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.

[0028] The second process conditions of the AlN epitaxial structure include: a growth pressure of 50-100 Torr, a V / III ratio of 10-1000, and a growth temperature of 1100-1300°C.

[0029] The epitaxial growth of the AlN merged layer of 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 the V / III ratio of the second growth stage, and the growth temperature of the first growth stage is higher than the growth temperature of the second growth stage.

[0030] The V / III ratio of the AlN epitaxial structure in the first growth stage is 10-100, and the growth temperature is 1200-1300°C; the V / III ratio of the second growth stage is 500-1000, and the growth temperature is 1100-1150°C.

[0031] As a specific example, the formation process of AlN epitaxial structure can be seen in Figure 2 As shown, AlN growth is generally performed by epitaxial growth on a heterogeneous substrate 100 with a mismatched lattice constant. This results in a high density of dislocations being generated at the interface between the substrate and AlN during the substrate nucleation stage due to the lattice mismatch. At this time, if holes are opened directly or when the AlN thickness is thin, the hole density will be large 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 to a certain extent before opening the hole. After experimental research by the inventors, the optimal range of this thickness is 600-750nm. If the thickness of the AlN base layer 110, i.e., the film layer marked as HTA1N1 in the figure, is thin, for example, within 100-200 nm, the initial AlN dislocation density is high, resulting in a high pore density. The tensile stress generated when the pores merge is large, which can easily lead to longer edge cracks. If the thickness of the HTA1N1 layer is too thick, for example, more than 0.8-1 μm, the dislocation density will be low, the number of pores will be reduced, and the number of dislocations annihilated will be reduced, which is not conducive to the final reduction of dislocation density. After multiple adjustments, the optimal value of the pore density is 1×10 19 -2×10 20 / cm 2 about.

[0032] After having a suitable thickness of HTA1N1 as preparation, with appropriate AlN growth conditions, hexagonal holes can be opened at the corresponding dislocations. The optimal growth conditions at this time are pressure 100-200Torr, V / III ratio 6000-10000, growth temperature 800-850℃, and growth rate controlled at 0.15-0.3 um / h. Under such hole opening conditions, hexagonal holes are more likely to be generated, and circular, diamond or irregular holes will not be randomly formed, which is crucial for the subsequent hole merging. The optimal thickness of the AlN formation layer 120, represented by the RnAlN thin layer in the figure, is 150-300 nm. If the thickness is too thin, the opening of the hole is smaller, and the lateral area of ​​the dislocation is reduced, which is not conducive to reducing the dislocation density. If the thickness is too thick, the holes tend to connect to form irregular holes, which will cause new dislocations to be generated when the holes merge later, which is also not conducive to reducing the dislocation density.

[0033] The function of the AlN merging layer 130, i.e., the film layer represented by HTA1N2 in the figure, is mainly to re-merge the holes opened by RnAlN, and to reduce the dislocation density by annihilating dislocations at the growth interface, while obtaining a smooth, crack-free and hole-free AlN surface. The HTAlN2 layer can be grown and merged under one condition until it is completely merged, or it can be divided into the HTAlN2-1 sublayer and the HTAlN2-2 sublayer, wherein the HTAlN2-1 sublayer is for quickly reducing the hexagonal holes but not completely merging, and the HTAlN2-2 sublayer slows down the merging speed based on the HTAlN2-1 sublayer, because too fast merging is likely to produce tensile stress, thereby causing cracks in AlN, so the optimal V / III of the HTAlN2-1 sublayer is 10-100, and the optimal V / III of the HTAlN2-2 sublayer is 500-1000; the optimal growth conditions for the growth of the HTAlN2 sublayer are a pressure of 50-100Torr and a growth temperature of 1200-1300°C; wherein the growth temperature of the HTAlN2-2 sublayer can be lower than that of the HTAlN2-1 sublayer.

[0034] However, it should be noted that although the two stages of different merging speeds are referred to as two "sub-layers" in the present invention, it is difficult to have a clear dividing line between the sub-layers in the actual epitaxial structure. The characteristics of different sub-layers are mainly reflected based on the different merging slopes of the hole structure in the layer.

[0035] A third aspect of the embodiments of the present invention further provides a semiconductor device, which includes the AlN epitaxial structure provided by any of the above embodiments and a functional structure constructed based on the AlN epitaxial structure.

[0036] 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 which are stacked in sequence. The first conductive semiconductor material layer and the second conductive semiconductor material layer have opposite conductive properties.

[0037] The technical solution of the present invention 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 the present invention, and do not limit the scope of the present invention.

[0038] Example 1 This embodiment illustrates a preparation process of an AlN epitaxial structure. Figure 3 As shown, the specific process includes: S1: Sputtering AlN bottom layer: Sputtering a 15 nm AlN film as the AlN bottom layer on the sapphire substrate 100 .

[0039] S2: The substrate 100 with the AlN bottom layer is placed in a MOCVD device, the temperature is raised to 1150° C., the pressure is 50 Torr, H2 and NH3 are introduced at the same time, and the AlN base layer 110 is grown, and the final thickness is 650 nm.

[0040] S3: growing AlN to form layer 120: lowering the growth temperature to 850°C, the pressure to 100 Torr, increasing the V / III ratio to 8000, and the growth rate to 0.15 um / h, and growing 300 nm AlN to form layer 120 at low temperature, slow speed, and high V / III.

[0041] S4: growing AlN merged layer 130: increasing the growth temperature to 1200° C., the pressure to 50 Torr, reducing the V / III ratio to 50, growing a 2000 nm AlN merged layer 130 at high temperature and low V / III to form pores inside the epitaxial structure.

[0042] Figure 4 The corresponding image is the surface hexagonal hole morphology image obtained by AFM measurement after the AlN formation layer 120 is grown. Figure 5 1 is an AFM image of the surface of the AlN merged layer 130 obtained after the growth is completed. It can be found that the hexagonal hole structure makes a positive contribution to the epitaxial quality of AlN, making it have excellent characteristics such as high flatness and low dislocation density.

[0043] Example 2 This embodiment illustrates a preparation process of an AlN epitaxial structure. Figure 6 As shown, the specific process includes: S1: Sputtering AlN bottom layer: Sputtering a 15 nm AlN film as the AlN bottom layer on the sapphire substrate 200 .

[0044] S2: The substrate 200 with the AlN bottom layer is placed in MOCVD, the temperature is raised to 1150° C., the pressure is 50 Torr, H2 and NH3 are introduced at the same time, and the AlN base layer 210 is grown, and the final thickness is 650 nm.

[0045] S3: growing AlN to form layer 220: lowering the growth temperature to 800°C, the pressure to 100 Torr, increasing the V / III ratio to 8000, and the growth rate to 0.15 um / h, growing 300 nm AlN to form layer 220 at low temperature, slow speed, and high V / III.

[0046] S4: growing the first merged sublayer 230: increasing the growth temperature to 1200° C., the pressure to 50 Torr, reducing the V / III ratio to 50, and growing a 500 nm first merged sublayer 230 at high temperature and low V / III to form pores inside the material.

[0047] S5: growing a second merged sublayer 240: increasing the growth temperature to 1150° C., the pressure to 50 Torr, the V / III ratio to 500, and growing a 1500 nm second merged sublayer 240 at high temperature and low V / III to form pores inside the material.

[0048] Since this embodiment adopts a two-stage merging method, the tensile stress generated by too fast merging is significantly reduced, so that the AlN epitaxial layer exhibits higher flatness and lower dislocation density.

[0049] Based on the above embodiments and comparative examples, it can be clearly seen that the technical solution provided by the embodiments of the present invention reduces the chance of irregular hole formation by appropriately controlling the thickness of the AlN base layer, adjusts the generation density of the hole structure, and guides the hole structure to tend to the same cross-sectional shape by controlling the growth conditions of the AlN formation layer, thereby preventing the hole structure from forming irregular and non-uniform cross-sectional shapes, avoiding alignment difficulties when the hole structures are merged, reducing the generation of new dislocations, and significantly improving the quality of the AlN epitaxial layer.

[0050] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An AlN epitaxial structure, characterized in that: It includes an AlN base layer, an AlN forming layer and an AlN merging layer which are sequentially stacked along a specified direction; The AlN base layer is a dense layer with a thickness of 600-750 nm; a plurality of hole structures are embedded in the AlN formation layer and the AlN merged layer, and along the specified direction, any of the hole structures opens in the AlN formation layer and closes in the AlN merged layer; Furthermore, if observed from the interface between the AlN forming layer and the AlN merging layer, the proportion of holes having the selected cross-sectional shape in all the hole structures is greater than 50%.

2. The AlN epitaxial structure according to claim 1, characterized in that: The hole density of the hole structure in the AlN merged layer is 1×10 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 comprises a continuous first portion and a second portion, and along the specified direction, the cross-sectional area of ​​the first portion has a tendency to gradually increase, and the cross-sectional area of ​​the second portion has a tendency to gradually decrease; Taking the designated direction as the height direction, the thickness of the AlN formation 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 portion; Or, the end of the second part is in an open state, the hole structure also includes a third part connected to the second part, and the hole structure is 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 change gradient, the cross-sectional area of ​​the third part has a second change gradient, and the absolute value of the first change gradient is greater than the absolute value of the second change gradient.

6. The AlN epitaxial structure according to claim 4, characterized in that: Taking the designated direction as the height direction, the height of the third portion is greater than the height of the second portion.

7. The AlN epitaxial structure according to claim 6, characterized in that: The invention also includes a substrate and an AlN bottom layer. The AlN bottom layer is formed on a surface of the substrate, and the AlN foundation layer is formed on a surface of the AlN bottom layer.

8. A method for preparing an AlN epitaxial structure, characterized in that: include: Epitaxially growing a dense AlN base layer, and controlling the growth thickness of the AlN base layer to be 600-750 nm; forming an AlN formation layer under a first process condition so that the AlN formation layer forms a plurality of open holes; The openings with the selected opening cross-sectional shape on the surface of the AlN formation layer account for more than 50% of all the opening holes; The AlN merged layer is grown under the second process, so that the open holes are gradually closed as the AlN merged layer gradually thickens, forming a closed hole structure.

9. The preparation method according to claim 8, characterized in that: The selected opening cross-sectional shape is a hexagon, and the first process conditions include: growth pressure of 100-200 Torr, V / III ratio of 6000-10000, growth temperature of 800-850° C., and growth rate of 0.15-0.3 um / h; And / or, the second process conditions include: growth pressure of 50-100 Torr, V / III ratio of 10-1000, and growth temperature of 1100-1300°C.

10. The preparation method according to claim 8, characterized in that: The epitaxial growth of the AlN merged layer is divided into a first growth stage and a second growth stage; The V / III ratio of the first growth stage is lower than the V / III ratio of the second growth stage, and the growth temperature of the first growth stage is higher than the growth temperature of the second growth stage.

11. The preparation method according to claim 10, characterized in that: The V / III ratio of the first growth stage is 10-100, and the growth temperature is 1200-1300°C; the V / III ratio of the second growth stage is 500-1000, and the growth temperature is 1100-1150°C.

12. A semiconductor device, characterized in that: The invention comprises the AlN epitaxial structure according to any one of claims 1 to 7 and a functional structure constructed based on the AlN epitaxial structure.

13. The semiconductor device according to claim 12, characterized in that The functional structure includes a first conductive semiconductor material layer, an active layer, and a second conductive semiconductor material layer which are stacked in sequence, and the first conductive semiconductor material layer and the second conductive semiconductor material layer have opposite conductive properties.

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