HEMT epitaxial wafer and preparation method thereof

Abstract

The present invention discloses a HEMT epitaxial wafer and a method for preparing the same. An aluminum nitride buffer layer is sputtered on a substrate, an undoped gallium nitride layer is grown on the aluminum nitride buffer layer, and then a single aluminum layer and an aluminum nitride layer are cyclically sputtered on the undoped gallium nitride layer. An N-type aluminum gallium nitride layer is grown on the cyclically sputtered epitaxial wafer. Therefore, sputtering a single aluminum nitride layer on an aluminum layer improves bonding capability. Simultaneously, cyclically sputtering the aluminum and aluminum nitride layers avoids the stress and low mobility issues associated with increasing thickness when using a single aluminum nitride layer, preventing a significant difference in quality between the center and edges of the epitaxial wafer. This increases the concentration of the two-dimensional electron gas (2DEG) by increasing the aluminum component while reducing interface defects without affecting 2DEG mobility.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a HEMT epitaxial wafer and a preparation method thereof. Background Art

[0002] Due to their advantages such as direct band gap, wide bandgap, and high breakdown electric field strength, materials such as GaN, AlGaN, and AlInGaN are widely used in fields such as electronic power and radio frequency devices. In particular, compared with traditional Si materials, semiconductors such as GaN, AlGaN, and AlInGaN are polar semiconductor materials. Therefore, when AlN and AlGaN materials are combined, fixed charges will exist at the interface of the two materials and a built-in electric field will spontaneously form, which can attract mobile carriers and thus form a two-dimensional electron gas. Therefore, HEMTs based on GaN materials have become a research hotspot for high-frequency power devices and power switches.

[0003] However, HEMTs based on GaN materials still have many problems. In particular, in order to increase the concentration of the two-dimensional electron gas at the interface, it is necessary to increase the Al component in the AlGaN barrier layer. However, at the same time, interface defects are introduced and the two-dimensional electron gas mobility is reduced, which greatly reduces the device performance of the HEMT. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a HEMT epitaxial wafer and a preparation method thereof, which can increase the concentration of two-dimensional electron gas while reducing interface defects without affecting the mobility of the two-dimensional electron gas.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A HEMT epitaxial wafer comprises an aluminum nitride buffer layer, a non-doped gallium nitride layer, a composite layer and an N-type aluminum gallium nitride layer grown in sequence on a substrate;

[0007] The composite layer includes an aluminum single layer and an aluminum nitride single layer that are cyclically sputtered according to a preset number of times.

[0008] A method for preparing a HEMT epitaxial wafer comprises the following steps:

[0009] sputtering an aluminum nitride buffer layer on a substrate, and growing an undoped gallium nitride layer on the aluminum nitride buffer layer;

[0010] cyclically sputtering an aluminum monolayer and an aluminum nitride monolayer on the undoped gallium nitride layer;

[0011] An N-type aluminum gallium nitride layer is grown on the cyclically sputtered epitaxial wafer.

[0012] The present invention has the beneficial effects of sputtering an aluminum nitride buffer layer on a substrate, growing an undoped gallium nitride layer on the aluminum nitride buffer layer, then cyclically sputtering an aluminum monolayer and an aluminum nitride monolayer on the undoped gallium nitride layer, and growing an N-type aluminum gallium nitride layer on the cyclically sputtered epitaxial wafer. Therefore, sputtering an aluminum nitride monolayer on an aluminum monolayer improves bonding capability. Simultaneously, cyclically sputtering an aluminum monolayer and an aluminum nitride monolayer avoids the stress and low mobility issues associated with increasing thickness of a single aluminum nitride layer, preventing a significant difference in quality between the center and edges of the epitaxial wafer. Consequently, increasing the aluminum component increases the two-dimensional electron gas concentration while reducing interface defects without affecting the two-dimensional electron gas mobility. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A structural diagram of a HEMT epitaxial wafer according to an embodiment of the present invention;

[0014] Figure 2 This is a flow chart of a method for preparing a HEMT epitaxial wafer according to an embodiment of the present invention;

[0015] Description of labels:

[0016] 1. Sapphire substrate; 2. Aluminum nitride buffer layer; 3. Undoped gallium nitride layer; 4. Aluminum single layer; 5. Aluminum nitride single layer; 6. N-type aluminum gallium nitride layer. DETAILED DESCRIPTION

[0017] To illustrate the technical content, achieved objectives and effects of the present invention in detail, the following description is given in conjunction with the embodiments and accompanying drawings.

[0018] Please refer to Figure 1 , an embodiment of the present invention provides a HEMT epitaxial wafer, comprising an aluminum nitride buffer layer, an undoped gallium nitride layer, a composite layer and an N-type aluminum gallium nitride layer grown sequentially on a substrate;

[0019] The composite layer includes an aluminum single layer and an aluminum nitride single layer that are cyclically sputtered according to a preset number of times.

[0020] As can be seen from the above description, the beneficial effects of the present invention are as follows: an aluminum nitride buffer layer is sputtered on a substrate, an undoped gallium nitride layer is grown on the aluminum nitride buffer layer, an aluminum monolayer and an aluminum nitride monolayer are then cyclically sputtered on the undoped gallium nitride layer, and an N-type aluminum gallium nitride layer is grown on the cyclically sputtered epitaxial wafer. Therefore, sputtering an aluminum nitride monolayer on an aluminum monolayer improves bonding capability. Simultaneously, cyclically sputtering an aluminum monolayer and an aluminum nitride monolayer avoids the stress and low mobility issues associated with increasing thickness of a single aluminum nitride layer, preventing a significant difference in quality between the center and edge of the epitaxial wafer. Consequently, increasing the aluminum component increases the two-dimensional electron gas concentration while reducing interface defects without affecting the two-dimensional electron gas mobility.

[0021] Furthermore, the thickness of the aluminum single layer is 0.1-1 nm.

[0022] From the above description, it can be seen that an aluminum single layer with a thickness of 0.1-1 nm can reduce the stress of the aluminum single layer, thereby reducing interface defects.

[0023] Furthermore, the thickness of the aluminum nitride single layer is 5-20 nm.

[0024] From the above description, it can be seen that an aluminum nitride single layer with a thickness of 5-20 nm can reduce the stress of the aluminum nitride single layer, thereby reducing interface defects.

[0025] Furthermore, the number of cycles of the composite layer is 15-60 times.

[0026] As can be seen from the above description, since the required thickness of the layer is relatively large, sputtering a single layer of aluminum and a single layer of aluminum nitride for 15-60 cycles can avoid the stress problem caused by using a single aluminum nitride layer.

[0027] Furthermore, the thickness of the undoped gallium nitride layer is 1-1.5 μm, and the thickness of the N-type aluminum gallium nitride layer is 250-300 nm.

[0028] Please refer to Figure 2 Another embodiment of the present invention provides a method for preparing a HEMT epitaxial wafer, comprising the steps of:

[0029] sputtering an aluminum nitride buffer layer on a substrate, and growing an undoped gallium nitride layer on the aluminum nitride buffer layer;

[0030] cyclically sputtering an aluminum monolayer and an aluminum nitride monolayer on the undoped gallium nitride layer;

[0031] An N-type aluminum gallium nitride layer is grown on the cyclically sputtered epitaxial wafer.

[0032] As can be seen from the above description, an aluminum nitride buffer layer is sputtered on the substrate, an undoped gallium nitride layer is grown on the aluminum nitride buffer layer, and then a single aluminum layer and a single aluminum nitride layer are cyclically sputtered on the undoped gallium nitride layer. Finally, an N-type aluminum gallium nitride layer is grown on the cyclically sputtered epitaxial wafer. Therefore, sputtering a single aluminum nitride layer on an aluminum layer improves bonding capability. Simultaneously, cyclically sputtering a single aluminum layer and a single aluminum nitride layer avoids the stress and low mobility issues associated with increasing thickness using a single aluminum nitride layer, preventing a significant difference in quality between the center and edges of the epitaxial wafer. Consequently, increasing the aluminum component increases the two-dimensional electron gas concentration while reducing interface defects without affecting the two-dimensional electron gas mobility.

[0033] Furthermore, growing an undoped gallium nitride layer on the aluminum nitride buffer layer comprises:

[0034] In a metal organic compound chemical vapor deposition device, at a temperature of 1100-1200° C., a mixed gas containing ammonia, hydrogen, and nitrogen and a trimethylgallium metal organic source are used to grow a non-doped gallium nitride layer with a thickness of 1-1.5 μm on the aluminum nitride buffer layer.

[0035] As can be seen from the above description, in the metal organic chemical vapor deposition equipment, a non-doped gallium nitride layer with a thickness of 1-1.5 μm is grown to facilitate the subsequent growth of other epitaxial structure layers.

[0036] Furthermore, after growing the undoped gallium nitride layer on the aluminum nitride buffer layer, the method further comprises:

[0037] The non-doped gallium nitride layer is annealed under the protection of ammonia and nitrogen, and the metal organic compound chemical vapor deposition is transferred out.

[0038] As can be seen from the above description, after the undoped gallium nitride layer is grown, annealing treatment is performed and the metal organic compound chemical vapor deposition is transferred out. Since hydrogen is required when the subsequent structure containing aluminum components is prepared in the metal organic compound chemical vapor deposition equipment, and the bonding ability between aluminum and hydrogen is strong, a large number of defects will be introduced. Therefore, the structure after the undoped gallium nitride layer is not prepared in the metal organic compound chemical vapor deposition, which can avoid the formation of interface defects.

[0039] Furthermore, cyclically sputtering an aluminum single layer and an aluminum nitride single layer on the undoped gallium nitride layer comprises:

[0040] Plasma enhanced chemical vapor deposition and chemical vapor deposition are cyclically used to sputter an aluminum single layer with a thickness of 0.1-1 nm and an aluminum nitride single layer with a thickness of 5-20 nm respectively on the non-doped gallium nitride layer.

[0041] From the above description, it can be seen that the epitaxial wafer is transferred to plasma enhanced chemical vapor deposition to sputter a single layer of aluminum, and then transferred to chemical vapor deposition to sputter a single layer of aluminum nitride. Sputtering aluminum nitride on the aluminum single layer can improve the bonding ability and form an aluminum nitride material with good crystal quality. At the same time, it can avoid the stress brought by the single aluminum nitride layer as the thickness increases, ensure that the quality difference between the center area and the edge of the entire epitaxial wafer is small, and improve the uniformity of the epitaxial wafer.

[0042] Furthermore, the step of growing an N-type aluminum gallium nitride layer on the cyclically sputtered epitaxial wafer comprises:

[0043] In a metal organic compound chemical vapor deposition device, a mixed gas containing ammonia and nitrogen is used, trimethylaluminum and diethyl gallium are used as metal organic sources, and silane is used as a doping gas to grow an N-type aluminum gallium nitride layer with a thickness of 250-300nm on a cyclically sputtered epitaxial wafer.

[0044] As can be seen from the above description, in a metal organic chemical vapor deposition device, growing an N-type aluminum gallium nitride layer with a thickness of 250-300 nm facilitates obtaining a complete HEMT epitaxial wafer.

[0045] The HEMT epitaxial wafer and its preparation method described above are suitable for improving AlGaN material defects in HEMT epitaxial wafers, effectively increasing the two-dimensional electron gas concentration and improving output power. The following describes a specific embodiment:

[0046] Example 1

[0047] Please refer to Figure 1 , a HEMT epitaxial wafer, comprising an aluminum nitride buffer layer, an undoped gallium nitride layer, a composite layer and an N-type aluminum gallium nitride layer grown sequentially on a substrate;

[0048] The composite layer includes an aluminum single layer and an aluminum nitride single layer that are cyclically sputtered according to a preset number of times.

[0049] Specifically, in this embodiment, the HEMT epitaxial wafer includes a 0.02 μm thick aluminum nitride buffer layer, a 1.5 μm thick undoped gallium nitride layer, a composite layer, and a 280 nm thick N-type aluminum gallium nitride layer grown sequentially on a substrate; the composite layer includes a 0.5 nm thick aluminum single layer and an 8 nm thick aluminum nitride single layer cyclically sputtered 20 times.

[0050] In other embodiments, the thickness of the undoped gallium nitride layer in the HEMT epitaxial wafer is 1-1.5 μm, the thickness of the N-type aluminum gallium nitride layer is 250-300 nm, the thickness of the aluminum single layer is 0.1-1 nm, and the thickness of the aluminum nitride single layer is 5-20 nm.

[0051] Example 2

[0052] Please refer to Figure 2 , a method for preparing a HEMT epitaxial wafer, comprising the steps of:

[0053] S1. sputtering an aluminum nitride buffer layer on a substrate, and growing an undoped gallium nitride layer on the aluminum nitride buffer layer.

[0054] S11. Using chemical vapor deposition (CVD) equipment, magnetron sputtering was performed with a high-purity Al target and argon, oxygen, and nitrogen plasma gases as reaction sources. A 0.02 μm thick AlN (aluminum nitride) film was sputtered on a non-PSS (Patterned Sapphire Substrate) sapphire (0001) surface at a temperature of 550°C.

[0055] S12. Using metal organic chemical vapor deposition (MOCVD) equipment, at a temperature of 1100-1200°C, using a mixed gas containing ammonia, hydrogen, and nitrogen, with a ratio of ammonia greater than or equal to 40%, and using trimethylgallium metal as an organic source, a non-doped gallium nitride layer with a thickness of 1-1.5 μm is grown on the aluminum nitride buffer layer.

[0056] S13, annealing the non-doped gallium nitride layer under the protection of ammonia and nitrogen, and transferring it out of the MOCVD.

[0057] S2. Cyclic sputtering of an aluminum single layer and an aluminum nitride single layer on the undoped gallium nitride layer.

[0058] Specifically, a single layer of Al is sputtered in plasma enhanced chemical vapor deposition (PECVD) with a thickness of about 0.1-1 nm, preferably 0.5 nm; then transferred to CVD to sputter an AlN film with a thickness of 5-20 nm, preferably 8 nm; the process of sputtering single layers of Al and AlN is cycled N times in total, with the number of cycles N being between 15 and 60 times, preferably 20 times.

[0059] S3. Growing an N-type aluminum gallium nitride layer on the cyclically sputtered epitaxial wafer.

[0060] Specifically, the epitaxial wafer that has completed the sputtering cycle is transferred to the MOCVD to grow a barrier layer N-type AlGaN with a thickness of 250-300nm; the gas used in the growth process is a mixed gas of ammonia and nitrogen, the proportion of ammonia is greater than or equal to 70%, the metal organic source is trimethylaluminum, diethyl gallium, and the doping gas is silane.

[0061] Afterwards, the epitaxial wafer is processed into a chip. First, the ohmic contact window is etched out, and a multi-layer electrode structure is evaporated to form the source and drain. Finally, the gate electrode is processed using photolithography, electron beam evaporation, and lift-off processes.

[0062] Therefore, this embodiment inserts a composite structure of cyclic sputtering of Al and AlN into the GaN and AlGaN layers of a traditional HEMT. Specifically, after the growth of the GaN channel layer is completed in MOCVD, the epitaxial wafer is transferred out of the MOCVD chamber after annealing in ammonia and nitrogen protection, transferred to PECVD to sputter a single layer of Al, and then transferred to CVD to sputter a single layer of AlN. AlN is sputtered on the Al single layer, thereby forming an AlN material with excellent crystal quality. At the same time, in order to avoid the stress brought by the single AlN layer as the thickness increases, resulting in a large difference in quality between the center and edge of the entire epitaxial wafer, resulting in poor epitaxial wafer uniformity; and during chip processing, the electrical property difference between the center and edge areas will bring complexity to the subsequent process.

[0063] Currently, there is a process for inserting AlN layers into GaN and AlGaN, which uses a continuous growth method in MOCVD. However, this method still introduces a large number of defects, and if PECVD is used for sputtering, there will be a problem of thin sputtering thickness. Therefore, this embodiment adopts a cyclic process of sputtering Al and sputtering AlN. On the basis of ensuring that the AlN has a certain thickness and good crystal quality, after the cyclic sputtering process is completed, it is transferred to MOCVD and then N-type AlGaN is grown. This can avoid the formation of interface defects and can also grow AlGaN material with a high Al content. The crystal quality is very good and can greatly improve the device performance of the HEMT.

[0064] In summary, the present invention provides a HEMT epitaxial wafer and its preparation method, which comprises sputtering an aluminum nitride buffer layer on a substrate using CVD; growing an undoped gallium nitride layer on the aluminum nitride buffer layer using MOCVD; then transferring the epitaxial wafer to a PECVD process to sputter a single layer of Al, then transferring it to a CVD process to sputter a single layer of AlN, repeating this cycle a preset number of times; and then transferring it to a MOCVD process to grow an N-type aluminum gallium nitride layer on the cyclically sputtered epitaxial wafer. Therefore, sputtering a single layer of aluminum nitride on an aluminum monolayer improves bonding ability, while cyclically sputtering a single layer of aluminum and aluminum nitride avoids the stress and low mobility issues associated with using a single aluminum nitride layer due to increased thickness, and prevents a significant difference in quality between the center and edge of the epitaxial wafer. This increases the two-dimensional electron gas concentration by increasing the aluminum component while reducing interface defects without affecting the two-dimensional electron gas mobility.

[0065] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a HEMT epitaxial wafer, characterized in that: Including steps: sputtering an aluminum nitride buffer layer on the substrate; In a metal organic compound chemical vapor deposition device, growing a non-doped gallium nitride layer on the aluminum nitride buffer layer; Annealing the undoped gallium nitride layer under the protection of ammonia and nitrogen, and transferring the undoped gallium nitride layer out of the metal organic chemical vapor deposition equipment; cyclically sputtering an aluminum single layer and an aluminum nitride single layer on the non-doped gallium nitride layer, wherein the aluminum single layer is sputtered in a plasma enhanced chemical vapor deposition process, and the aluminum nitride single layer is sputtered in a chemical vapor deposition process; In a metal organic chemical vapor deposition device, an N-type aluminum gallium nitride layer is grown on a cyclically sputtered epitaxial wafer.

2. The method for preparing a HEMT epitaxial wafer according to claim 1, wherein: Growing an undoped gallium nitride layer on the aluminum nitride buffer layer comprises: At a temperature of 1100-1200° C., a non-doped gallium nitride layer with a thickness of 1-1.5 μm is grown on the aluminum nitride buffer layer using a mixed gas containing ammonia, hydrogen, and nitrogen and a trimethylgallium metal organic source.

3. The method for preparing a HEMT epitaxial wafer according to claim 1, wherein: Cyclic sputtering of an aluminum monolayer and an aluminum nitride monolayer on the undoped gallium nitride layer comprises: Plasma enhanced chemical vapor deposition and chemical vapor deposition are cyclically used to sputter an aluminum single layer with a thickness of 0.1-1 nm and an aluminum nitride single layer with a thickness of 5-20 nm respectively on the non-doped gallium nitride layer.

4. The method for preparing a HEMT epitaxial wafer according to claim 1, wherein: The step of growing an N-type aluminum gallium nitride layer on the cyclically sputtered epitaxial wafer comprises: A mixed gas containing ammonia and nitrogen is used, trimethylaluminum and diethyl gallium are used as metal organic sources, and silane is used as a doping gas to grow an N-type aluminum gallium nitride layer with a thickness of 250-300nm on a cyclically sputtered epitaxial wafer.

5. A HEMT epitaxial wafer prepared by the HEMT epitaxial wafer preparation method according to any one of claims 1 to 4, characterized in that: The method comprises an aluminum nitride buffer layer, a non-doped gallium nitride layer, a composite layer and an N-type aluminum gallium nitride layer grown in sequence on a substrate; The composite layer includes an aluminum single layer and an aluminum nitride single layer that are sputtered cyclically for a preset number of times, and the number of cycles for the composite layer is 15-60 times.

6. The HEMT epitaxial wafer according to claim 5, characterized in that: The thickness of the aluminum single layer is 0.1-1 nm.

7. The HEMT epitaxial wafer according to claim 5, characterized in that: The thickness of the aluminum nitride single layer is 5-20 nm.

8. The HEMT epitaxial wafer according to claim 5, characterized in that: The thickness of the undoped gallium nitride layer is 1-1.5 μm, and the thickness of the N-type aluminum gallium nitride layer is 250-300 nm.

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