Formation method of power device
By performing neutron transmutation doping and cooling treatment on the gallium nitride epitaxial layer, the problem of carbon element doping in the epitaxial layer is solved, the breakdown voltage and service life of the power device are improved, the process flow is simplified and the process is reduced. Leakage current and impurity pollution.
Patent Information
- Application Number
- CN202411248909.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-06
- Publication Date
- 2024-12-10
AI Technical Summary
During the manufacturing process of power devices, the unevenness of carbon doping in the epitaxial layer leads to breakdown voltage and leakage current problems, and conventional methods have strong dependence on gas flow and temperature conditions, which can easily lead to warping of semiconductor substrates and affect the device Yield rate.
By performing neutron transmutation doping on the gallium nitride epitaxial layer, the nitrogen element absorbs neutrons into carbon elements is used to transmutate neutrons into carbon elements, combined with cooling treatment to improve the uniformity of carbon elements and avoid impurities during the formation process. pollution.
The uniform doping of carbon elements in the gallium nitride epitaxial layer is achieved, which improves the breakdown voltage and service life of the device, while reducing leakage current and impurity pollution, and simplifying the process flow.
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Figure CN119108278A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for forming a power device. Background Art
[0002] In the manufacturing process of power devices, in order to improve the breakdown voltage of the device and reduce the leakage current, it is usually necessary to perform high-resistance doping treatment on the epitaxial layer in the device, for example, using carbon as the doping element. At present, the conventional method of doping carbon elements in the epitaxial layer includes using hydrocarbons produced by the decomposition of TMG (trimethylgallium) as a doping source for intrinsic doping, or using carbon-containing dopants (such as methyl halides) for non-intrinsic doping. However, these methods are highly dependent on the gas flow rate and temperature conditions during implementation. At the same time, in a high-temperature growth environment, the surface of the semiconductor substrate is prone to warping, which can easily lead to uneven carbon doping in the epitaxial layer, thereby affecting the breakdown voltage and leakage current of the device and reducing the yield of the device. Summary of the invention
[0003] The object of the present invention is to provide a method for forming a power device to improve the uniformity of carbon elements doped in an epitaxial layer.
[0004] To achieve the above object, the present invention provides a method for forming a power device, comprising:
[0005] Providing a semiconductor substrate, on which a gallium nitride epitaxial layer is formed;
[0006] Performing neutron transmutation doping treatment on the gallium nitride epitaxial layer to dope carbon elements in the gallium nitride epitaxial layer;
[0007] The semiconductor substrate is subjected to a cooling process.
[0008] Optionally, in the method for forming the power device, during the neutron transmutation doping process, a thermal neutron beam is used to irradiate the gallium nitride epitaxial layer so that the nitrogen element in the gallium nitride epitaxial layer absorbs neutrons and transmutes into the carbon element.
[0009] Optionally, in the method for forming a power device, the thermal neutron irradiation amount of the neutron transmutation doping treatment is 5×10 16 cm -2 Up to 5×10 19 cm -2 , the irradiation flux is 1×10 13 cm -2 s -1 Up to 1×10 14 cm -2 s -1 , the irradiation time is 28 hours to 30 hours.
[0010] Optionally, in the method for forming a power device, a method for cooling the semiconductor substrate includes:
[0011] The semiconductor substrate having the gallium nitride epitaxial layer is placed in a constant temperature nitrogen cabinet for a predetermined time, wherein the predetermined time is 288 hours to 360 hours.
[0012] Optionally, in the method for forming a power device, after cooling the semiconductor substrate, the method for forming a power device further includes:
[0013] A channel layer, a barrier layer and a gate layer are sequentially formed on the gallium nitride epitaxial layer, and the channel layer covers the gallium nitride epitaxial layer.
[0014] Optionally, in the method for forming the power device, the material of the channel layer includes gallium nitride, and the channel layer is formed by metal organic compound chemical vapor deposition, and the process temperature when forming the channel layer is 1000° C. to 1010° C.
[0015] Optionally, in the method for forming a power device, the material of the barrier layer includes aluminum gallium nitride, and the barrier layer is formed by a metal organic compound chemical vapor deposition process, and the process temperature when forming the barrier layer is 1000° C. to 1050° C.
[0016] Optionally, in the method for forming a power device, the material of the gate layer includes gallium nitride, and the gate layer is formed by a metal organic compound chemical vapor deposition process, and the process temperature when forming the gate layer is 950° C. to 980° C.
[0017] Optionally, in the method for forming the power device, a nucleation layer is further formed between the semiconductor substrate and the gallium nitride epitaxial layer, the nucleation layer covers the semiconductor substrate, and the gallium nitride epitaxial layer covers the nucleation layer.
[0018] Optionally, in the method for forming a power device, the material of the nucleation layer includes aluminum nitride.
[0019] In the method for forming a power device provided by the present invention, a neutron transmutation doping treatment is performed on the gallium nitride epitaxial layer to dope carbon in the gallium nitride epitaxial layer. During the neutron transmutation doping treatment, the nitrogen element in the gallium nitride epitaxial layer absorbs neutrons and transmutes into carbon. Since the nitrogen and gallium elements in the gallium nitride epitaxial layer are distributed more evenly, and the penetration depth of neutrons in the gallium nitride epitaxial layer is large, it can penetrate deeply into the interior of the gallium nitride epitaxial layer. Therefore, the neutron transmutation doping treatment can achieve uniform carbon doping in the gallium nitride epitaxial layer, thereby improving the uniformity of the carbon element in the gallium nitride epitaxial layer. In addition, during the neutron transmutation doping treatment, the carbon element in the gallium nitride epitaxial layer is transmuted by the nitrogen element, rather than directly introduced by doping, so that other impurity elements (such as hydrogen and halogen elements) can be prevented from entering the gallium nitride epitaxial layer, reducing or avoiding the contamination of the gallium nitride epitaxial layer by other impurity elements (such as hydrogen and halogen elements). BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 is a schematic flow chart of a method for forming a power device provided in an embodiment of the present invention;
[0021] Figures 2 to 6 is a schematic diagram of a structure formed in a method for forming a power device provided in an embodiment of the present invention;
[0022] The reference numerals are described as follows:
[0023] 100 - semiconductor substrate; 101 - nucleation layer; 102 - gallium nitride epitaxial layer; 103 - channel layer; 104 - barrier layer; 105 - gate layer; 110 - neutrons. DETAILED DESCRIPTION
[0024] The following is a further detailed description of the method for forming a power device proposed in the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the accompanying drawings are in a very simplified form and are not in precise proportions, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.
[0025] Figure 1 FIG. 1 is a flow chart of a method for forming a power device provided by an embodiment of the present invention. Figure 1 As shown, the method for forming a power device provided in this embodiment includes:
[0026] Step S1: providing a semiconductor substrate, on which a gallium nitride epitaxial layer is formed;
[0027] Step S2: performing neutron transmutation doping treatment on the gallium nitride epitaxial layer to dope carbon elements in the gallium nitride epitaxial layer;
[0028] Step S3: Cooling the semiconductor substrate.
[0029] Figures 2 to 6 Schematic diagram of the structure formed in the method for forming a power device provided in an embodiment of the present invention; Figures 2 to 6 The method for forming the power device provided in this embodiment is described in more detail.
[0030] First, refer to Figure 2 As shown, step S1 is performed to provide a semiconductor substrate 100, on which a gallium nitride epitaxial layer 102 is formed. The semiconductor substrate 100 can be a silicon (Si) substrate, a gallium nitride (GaN) substrate, a silicon carbide (SiC) substrate, a gallium oxide (Ga2O3) substrate, a diamond substrate or a sapphire substrate. In this embodiment, the semiconductor substrate 100 is a silicon substrate.
[0031] The formed GaN epitaxial layer 102 is, for example, a device layer for preparing a device, and in a subsequent process, a power device can be prepared using the GaN epitaxial layer 102. Alternatively, the GaN epitaxial layer 102 can also be used as a bottom buffer layer of a device layer, and in a subsequent process, a device layer can be further epitaxially grown on the GaN epitaxial layer 102 for device processing.
[0032] In this embodiment, the material of the gallium nitride epitaxial layer 102 is undoped gallium nitride (GaN), and the gallium nitride epitaxial layer 102 can be formed by metal organic chemical vapor deposition (MOCVD) process, and the growth temperature of the gallium nitride epitaxial layer 102 can be 1000° C. to 1100° C. The thickness of the gallium nitride epitaxial layer 102 can be 3 μm to 5 μm.
[0033] In this embodiment, Figure 2 As shown, before forming the gallium nitride epitaxial layer 102, a nucleation layer 101 is formed on the semiconductor substrate 100. The gallium nitride epitaxial layer 102 is grown based on the nucleation layer 101. The nucleation layer 101 can provide a nucleation center for the subsequent growth of the gallium nitride epitaxial layer 102 to reduce the interface free energy between the gallium nitride epitaxial layer 102 and the semiconductor substrate 100, thereby improving the adsorption capacity of the gallium nitride epitaxial layer 102, and then obtaining a gallium nitride epitaxial layer 102 with good film quality, thereby ensuring the working performance of the device subsequently manufactured based on the gallium nitride epitaxial layer 102.
[0034] Exemplarily, the material of the nucleation layer 101 includes aluminum nitride, and the nucleation layer 101 can be formed by a metal organic chemical vapor deposition process (MOCVD), and the process gas for forming the nucleation layer 101 includes trimethylaluminum (TMAl), ammonia (NH3), nitrogen and hydrogen. The thickness of the nucleation layer 101 can be 0.2 μm to 0.22 μm.
[0035] Next, step S2 is performed to perform neutron transmutation doping treatment on the GaN epitaxial layer 102 to dope carbon elements in the GaN epitaxial layer 102 .
[0036] In this embodiment, during the neutron transmutation doping process, a thermal neutron beam is used to irradiate the gallium nitride epitaxial layer 102, so that the nitrogen element in the gallium nitride epitaxial layer 102 absorbs the neutrons 110 in the thermal neutron beam and transmutes into carbon element, that is, part of the nitrogen element in the gallium nitride epitaxial layer 102 undergoes a nuclear reaction under the influence of the thermal neutron beam irradiation, so that part of the nitrogen atoms in the gallium nitride epitaxial layer 102 capture neutrons 110 and decay into carbon atoms, thereby achieving carbon doping.
[0037] Specifically, during the neutron transmutation doping process, the nitrogen element in the GaN epitaxial layer 102 absorbs a neutron and transmutes into a carbon element, and releases a proton. The specific reaction formula is as follows:
[0038]
[0039] in, Expressed as nitrogen, Represented as neutron, Represented as the element carbon, Represented as protons.
[0040] It should be noted that during the neutron transmutation doping process, the gallium element in the GaN epitaxial layer 102 absorbs a neutron and becomes an isotope. The half-life is about 20 minutes. In the subsequent process, Continue to decay and become germanium, specifically The specific reaction process is as follows:
[0041]
[0042] in, and Expressed as different isotopes of the element gallium, Represented as neutron, Represented as the element germanium.
[0043] During the neutron transmutation doping process, the capture cross section of gallium is larger than that of nitrogen due to the larger atomic radius of gallium. Therefore, gallium is more likely to collide with neutrons during the neutron transmutation doping process, thereby producing germanium. Similarly, the capture cross section of the produced germanium is also larger, and it is also easier to collide with neutrons. Therefore, the formed germanium absorbs a neutron under the bombardment of neutrons and becomes an isotope. The half-life is 264 hours. In the subsequent process, Continues to decay and decays into isotopes of gallium The specific reaction process is as follows:
[0044]
[0045] Finally, the GaN epitaxial layer 102 retains the carbon element that is transmuted by the nitrogen element absorbing neutrons. That is carbon-14. Since the half-life of carbon-14 is as long as about 5730 years, which is much longer than the half-life of gallium and germanium isotopes, and also much longer than the working life of ordinary semiconductor devices (such as power devices), for semiconductor devices, carbon-14 can be regarded as a stable existence, which is beneficial to improve the overall stability of the device.
[0046] That is, during the neutron transmutation doping process, the nitrogen element in the gallium nitride epitaxial layer 102 absorbs a neutron and transmutes into a carbon element, that is, the neutron undergoes a nuclear reaction with the nitrogen element in the gallium nitride epitaxial layer 102, thereby forming a carbon element. Since gallium nitride is a crystal, the distribution of isotope atoms in the crystal is very uniform, so the distribution of nitrogen and gallium elements in the gallium nitride epitaxial layer is relatively uniform, and the penetration depth of neutrons in the gallium nitride epitaxial layer is large, and it can penetrate deeply into the interior of the gallium nitride epitaxial layer 102. Therefore, through the neutron transmutation doping process, uniform carbon doping can be achieved in the gallium nitride epitaxial layer, thereby improving the uniformity of the carbon element in the gallium nitride epitaxial layer, thereby improving the breakdown voltage of the device and reducing the leakage current.
[0047] After the gallium nitride epitaxial layer 102 is subjected to neutron transmutation doping treatment, the carbon element in the gallium nitride epitaxial layer is detected, and it is found that the concentration uniformity of the carbon element (or carbon impurities) in the gallium nitride epitaxial layer 102 is less than 3%. It can be seen that the distribution of the carbon element in the gallium nitride epitaxial layer 102 is relatively uniform, and there will be no large carbon element concentration gradient or local aggregation phenomenon.
[0048] In addition, due to the carbon element retained in the GaN epitaxial layer 102 The decay period is longer ( The decay period is about 5730 years). Therefore, by performing neutron transmutation doping on the GaN epitaxial layer, not only can uniform carbon doping be achieved in the GaN epitaxial layer 102, but also the service life of the power device can be increased.
[0049] In this embodiment, the thermal neutron irradiation amount of the neutron transmutation doping treatment is 5×10 16 cm -2 Up to 5×10 19 cm -2 , the irradiation flux is 1×10 13 cm -2 s -1 Up to 1×10 14 cm -2 s -1 The irradiation time is 28 hours to 30 hours to control the carbon content in the GaN epitaxial layer 102 to meet the device use standard and ensure that the entire GaN epitaxial layer 102 can be doped during the neutron transmutation doping process, which is conducive to making the carbon element in the GaN epitaxial layer 102 more uniform. In addition, during the neutron transmutation doping process, other impurity elements (such as hydrogen and halogen elements) can be prevented from entering the GaN epitaxial layer 102, reducing or avoiding the contamination of the GaN epitaxial layer 102 by other impurity elements (such as hydrogen and halogen elements).
[0050] Next, step S3 is performed to cool the semiconductor substrate 100. Specifically, the method for cooling the semiconductor substrate 100 includes: placing the semiconductor substrate 100 having the gallium nitride epitaxial layer 102 in a constant temperature nitrogen cabinet for a predetermined time, that is, placing the semiconductor substrate 100 having the gallium nitride epitaxial layer 102 in a nitrogen environment for cooling, so that the cleanliness of the surface of the gallium nitride epitaxial layer 102 can be ensured, and the gallium nitride epitaxial layer 102 can be prevented from being oxidized, thereby avoiding the formation of a natural oxide layer on the surface of the gallium nitride epitaxial layer 102. At the same time, placing the semiconductor substrate 100 having the gallium nitride epitaxial layer 102 in a nitrogen environment can also speed up the cooling speed. Among them, the predetermined time is 288 hours to 360 hours.
[0051] In this embodiment, since the GaN epitaxial layer 102 and the semiconductor substrate 100 have certain radioactivity after the aforementioned neutron transmutation doping treatment, the semiconductor substrate 100 is cooled until the radioactivity of the GaN epitaxial layer 102 and the semiconductor substrate 100 is reduced to a preset threshold value, so that the radiation amount of the GaN epitaxial layer 102 and the semiconductor substrate 100 is reduced to a safe range, wherein the preset threshold value is 1×10 -6 Ci / g.
[0052] Furthermore, in the aforementioned neutron transmutation doping process, the gallium element in the gallium nitride epitaxial layer 102 absorbs a neutron and becomes an isotope. after, It will continue to decay into germanium. During the neutron transmutation doping process, germanium will be bombarded by neutrons and become an isotope of germanium with a half-life of about 264 hours. Subsequent isotopes of germanium Will continue to decay into isotopes of gallium Therefore, by cooling the GaN epitaxial layer 102, it can be ensured that the germanium element in the GaN epitaxial layer 102 decays into the gallium element. In this way, the doping of impurities other than carbon into the GaN epitaxial layer 102 can be reduced or avoided.
[0053] In this embodiment, after the semiconductor substrate 100 is cooled, that is, after the radioactivity of the GaN epitaxial layer 102 and the semiconductor substrate 100 is reduced to a preset threshold, the semiconductor substrate 100 with the GaN epitaxial layer 102 is rewired.
[0054] like Figure 4 As shown, after the semiconductor substrate 100 is cooled, a channel layer 103 is formed on the gallium nitride epitaxial layer 102, and the channel layer 103 covers the gallium nitride epitaxial layer 102. Since the channel layer 103 is formed on the gallium nitride epitaxial layer 102, the gallium nitride epitaxial layer 102 can play a buffering role, and can reduce the lattice mismatch between the two when the channel layer is directly epitaxially grown on the semiconductor substrate 100, thereby reducing the density of crystal defects such as dislocations, and improving the film quality of the channel layer to ensure the working performance of the device.
[0055] In this embodiment, the material of the channel layer 103 includes gallium nitride (GaN), and the channel layer 103 is formed by a metal organic compound chemical vapor deposition process, and the process temperature when forming the channel layer 103 is 1000°C to 1010°C, for example, 1050°C. In the aforementioned neutron transmutation doping process, there are also recoil effects such as neutron bombardment and gamma radiation, which can easily lead to the generation of interstitial atoms or defects in the gallium nitride epitaxial layer 102, thereby damaging the lattice of the gallium nitride epitaxial layer 102. Therefore, the process temperature when forming the channel layer 103 is 1000°C to 1010°C, so that not only the epitaxial growth of the channel layer 103 can be achieved, but also the lattice damage of the gallium nitride epitaxial layer 102 caused by the aforementioned neutron transmutation doping process can be repaired, without the need for an additional high-temperature annealing step, thereby simplifying the process steps.
[0056] like Figure 5As shown, after forming the channel layer 103, a barrier layer 104 is formed on the channel layer 103, and the barrier layer 104 covers the channel layer 103. The barrier layer 104 is used to prevent the free flow of electrons and holes between different layers, which helps to control the distribution of carriers, thereby optimizing the performance of the device. The material of the barrier layer 104 includes aluminum gallium nitride (AlGaN), and the barrier layer 104 is formed by a metal organic compound chemical vapor deposition process. The process temperature when forming the barrier layer 104 is 1000°C to 1050°C.
[0057] Benru Figure 6 As shown, after the barrier layer 104 is formed, a gate layer 105 is formed on the barrier layer 104, and the gate layer 105 covers the barrier layer 104. The gate layer 105 is made of gallium nitride (GaN), and is formed by a metal organic chemical vapor deposition process. The process temperature when forming the gate layer 105 is 950° C. to 980° C. The conductivity type of the gate layer 105 may be P type.
[0058] In this embodiment, the channel layer 103, the barrier layer 104, the gate layer 105, the gallium nitride epitaxial layer 102 and the nucleation layer 101 can all be formed by a metal organic compound chemical vapor deposition process. In this way, when forming the channel layer 103, the barrier layer 104, the gate layer 105, the gallium nitride epitaxial layer 102 and the nucleation layer 101, it can be completed in the same reaction chamber, that is, the channel layer 103, the barrier layer 104, the gate layer 105, the gallium nitride epitaxial layer 102 and the nucleation layer 101 are in-situ epitaxially grown, which can avoid the appearance of a natural oxide layer on the surface of these film layers.
[0059] In summary, in the method for forming a power device provided by the present invention, a neutron transmutation doping treatment is performed on the gallium nitride epitaxial layer to dope carbon elements in the gallium nitride epitaxial layer. During the neutron transmutation doping treatment, the nitrogen elements in the gallium nitride epitaxial layer absorb neutrons and transmute into carbon elements. Since the nitrogen elements and gallium elements in the gallium nitride epitaxial layer are distributed more evenly, and the penetration depth of neutrons in the gallium nitride epitaxial layer is large, it can penetrate deeply into the interior of the gallium nitride epitaxial layer. Therefore, the neutron transmutation doping treatment can achieve uniform carbon doping in the gallium nitride epitaxial layer, thereby improving the uniformity of the carbon elements in the gallium nitride epitaxial layer. In addition, during the neutron transmutation doping treatment, other impurity elements (such as hydrogen and halogen elements) can be prevented from entering the gallium nitride epitaxial layer, reducing or avoiding the contamination of the gallium nitride epitaxial layer by other impurity elements (such as hydrogen and halogen elements). Moreover, it is fully compatible with the neutron transmutation doping process and does not require the development of new processes or equipment.
[0060] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.
[0061] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.
Claims
1. A method for forming a power device, characterized in that: include: Providing a semiconductor substrate, on which a gallium nitride epitaxial layer is formed; Performing neutron transmutation doping treatment on the gallium nitride epitaxial layer to dope carbon elements in the gallium nitride epitaxial layer; The semiconductor substrate is subjected to a cooling process.
2. The method for forming a power device according to claim 1, wherein: During the neutron transmutation doping process, the gallium nitride epitaxial layer is irradiated with a thermal neutron beam, so that the nitrogen element in the gallium nitride epitaxial layer absorbs neutrons and transmutes into the carbon element.
3. The method for forming a power device according to claim 2, wherein: The thermal neutron irradiation amount of the neutron transmutation doping treatment is 5×10 16 cm -2 Up to 5×10 19 cm -2 , the irradiation flux is 1×10 13 cm -2 s -1 Up to 1×10 14 cm -2 s -1 The irradiation time is 28 hours to 30 hours.
4. The method for forming a power device according to claim 1, wherein: The method for cooling the semiconductor substrate comprises: The semiconductor substrate having the gallium nitride epitaxial layer is placed in a constant temperature nitrogen cabinet for a predetermined time, wherein the predetermined time is 288 hours to 360 hours.
5. The method for forming a power device according to claim 1, wherein: After the semiconductor substrate is cooled, the method for forming a power device further includes: A channel layer, a barrier layer and a gate layer are sequentially formed on the gallium nitride epitaxial layer, and the channel layer covers the gallium nitride epitaxial layer.
6. The method for forming a power device according to claim 5, wherein: The material of the channel layer includes gallium nitride, and the channel layer is formed by a metal organic compound chemical vapor deposition process, and the process temperature when forming the channel layer is 1000° C. to 1010° C.
7. The method for forming a power device according to claim 5, wherein: The material of the barrier layer includes aluminum gallium nitride, and the barrier layer is formed by a metal organic compound chemical vapor deposition process, and the process temperature when forming the barrier layer is 1000° C. to 1050° C.
8. The method for forming a power device according to claim 5, wherein: The gate layer is made of gallium nitride and is formed by a metal organic chemical vapor deposition process. The process temperature for forming the gate layer is 950° C. to 980° C.
9. The method for forming a power device according to claim 1, wherein: A nucleation layer is further formed between the semiconductor substrate and the gallium nitride epitaxial layer. The nucleation layer covers the semiconductor substrate, and the gallium nitride epitaxial layer covers the nucleation layer.
10. The method for forming a power device according to claim 9, wherein: The material of the nucleation layer includes aluminum nitride.