Laser annealing silicon carbide ohmic contact, device and preparation method thereof

Abstract

The invention belongs to the field of semiconductor devices, and relates to a laser annealing silicon carbide ohmic contact, a device and a preparation method thereof. RCA standard cleaning is carried out on the N-type 4H-SiC substrate, and two epitaxial layers, namely a buffer layer and an N-type doping layer, are arranged on the N-type 4H-SiC substrate; manufacturing a P-type doped region and an N-type doped region in the 4H-SiC epitaxial layer by adopting an ion implantation method, and performing rapid thermal annealing to obtain an epitaxial wafer; and depositing a metal layer above the P-type region and the N-type region of the epitaxial wafer to form a source electrode, and performing high-energy laser annealing on the source electrode region to form ohmic contact. Through the cooperation of the Al / Ti / Ni or Ni / Ti metal system and the laser annealing process, under the high energy density, the metal and silicon carbide react to form a compound, and silicon is formed on an interface at the same time, so that the ohmic contact effect is effectively improved, and N-type and P-type ohmic contact can be realized at the same time.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor devices and relates to a laser annealed silicon carbide ohmic contact, a device and a preparation method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] In recent years, with the rapid expansion of the electric vehicle market and the growing demand for efficient and compact power electronic converters, the demand for SiC MOSFET (metal oxide semiconductor field effect transistor) has continued to rise. At the same time, the technology of SiC MOSFET has also been continuously improving, including the optimization of device structure (such as planar and planar trench structures), improved gate oxide reliability, faster switching speed, and reduced switching losses. Although SiC MOSFET has many advantages, its high cost and complex manufacturing process are still the key factors hindering its large-scale application. Therefore, how to reduce costs and increase production has become the focus of current research. Among them, laser annealing, as an emerging annealing process, is superior to the existing rapid thermal annealing process in production efficiency, so it has always been a hot topic of research. At present, the application of laser annealing process in silicon carbide is in the back metal ohmic contact process of Schottky diode, but it is only for N-type silicon carbide, while the MOSFET process has a P-type doped area in addition to N-type doped silicon carbide in the source metal region. In order to realize both N-type and P-type ohmic contact processes at the same time, the conventional rapid thermal annealing process takes a compromise temperature in the annealing process to achieve both at the same time, but it causes the ohmic contact effect of both to decrease. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a laser annealed silicon carbide ohmic contact, device and preparation method thereof. The present invention uses Al / Ti / Ni (aluminum / titanium / nickel) or Ni / Ti (nickel / titanium) metal system and laser annealing process to form a composite with metal and silicon carbide at high energy density, and at the same time, silicon is formed at the interface, which effectively improves the ohmic contact effect and can realize N-type and P-type ohmic contacts at the same time. Compared with the RTP (rapid annealing process) process, the specific contact resistivity of the P-type ohmic contact is reduced by 2 orders of magnitude while ensuring the specific contact resistivity of the N-type.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for preparing a laser annealed silicon carbide ohmic contact, comprising: Performing RCA standard cleaning on an N-type 4H-SiC (silicon carbide) substrate, on which two epitaxial layers are arranged, namely a buffer layer and an N-type doping layer; Using ion implantation to form a P-type doping region and an N-type doping region in a 4H-SiC epitaxial layer, and performing rapid thermal annealing to obtain an epitaxial wafer; A metal layer is deposited on the P-type and N-type regions of the epitaxial wafer to form a source electrode, and high-energy laser annealing is performed on the source electrode region to form an ohmic contact.

[0006] The thickness of the doping layer will affect the performance of the SiC MOSFET. Therefore, the thickness of the doping layer is studied in the present invention. Preferably, the thickness of the N-type doping layer is 10 μm-25 μm.

[0007] When ion implantation is performed in the SiC epitaxial layer, nitrogen (N) or phosphorus (P), which are donor elements that easily reduce resistance, is usually used for the N-type region, while aluminum (Al) is usually used as an acceptor element for the P-type region. Therefore, preferably, the ions implanted by the ion implantation method are nitrogen ions and aluminum ions, respectively.

[0008] The rapid thermal annealing process can repair the crystal lattice and activate the doped ions. Therefore, the present invention studies the temperature of the rapid thermal annealing process. Preferably, the temperature of the rapid thermal annealing is 1600°C-1650°C.

[0009] The selection of contact materials can improve the ohmic contact performance. To this end, the present invention has found through systematic research and experimental exploration that during laser annealing, Al / Ti / Ni or Ni / Ti reacts with silicon carbide to form a composite and simultaneously forms Si (silicon), which significantly improves the ohmic contact effect. Therefore, preferably, the metal layer is an Al / Ti / Ni composite metal layer or a Ni / Ti composite metal layer.

[0010] The study found that when the source region is subjected to high-energy laser annealing, if the instantaneous temperature of the laser energy reaches above 2000°C, the metal and silicon carbide react to form a composite (where Ni and Si react to form a nickel-silicon composite, and Ti, Al and carbon react to form a copolymer), while Si is formed at the interface, effectively reducing the contact resistance. Therefore, preferably, the laser annealing conditions are a laser wavelength of 248nm-532nm and an energy density of 2.5J / cm 2 -2.75J / cm 2 .

[0011] The second aspect of the present invention provides an ohmic contact formed by the above method.

[0012] The third aspect of the present invention provides a method for preparing a device, comprising: Performing RCA standard cleaning on an N-type 4H-SiC substrate, wherein two epitaxial layers are arranged on the N-type 4H-SiC substrate, namely a buffer layer and an N-type doping layer; Using ion implantation to form a P-type doping region and an N-type doping region in a 4H-SiC epitaxial layer, and performing rapid thermal annealing to obtain an epitaxial wafer; Preparing and patterning a gate oxide layer region above the epitaxial wafer; Depositing polysilicon or metal in the gate region for use as a gate electrode; Depositing a metal layer on the P-type and N-type regions of the epitaxial wafer to form a source electrode, and performing laser annealing on the source electrode region to form an ohmic contact; Metal Ni is deposited on the back of the epitaxial wafer to form a drain electrode, and laser annealing is performed on the drain electrode area to form an ohmic contact.

[0013] Preferably, the laser annealing conditions are: the laser wavelength is 248nm-532nm, the energy density is 1.8J / cm 2 -2.75J / cm 2 .

[0014] The fourth aspect of the present invention provides a device prepared by the above method.

[0015] Beneficial effects of the present invention (1) The present invention combines the Al / Ti / Ni or Ni / Ti metal system with the laser annealing process to form a composite with metal and silicon carbide at a high energy density, thereby effectively improving the ohmic contact effect and achieving both N-type and P-type ohmic contacts.

[0016] (2) The preparation method of the present invention is simple, the device resistance is small, the practicability is strong, and it is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0018] Figure 1 It is a schematic diagram of the structure after epitaxy and ion implantation of the present invention; Figure 2 This is a schematic diagram of the gate oxide layer and the electrode after preparation of the present invention; Figure 3 It is a complete schematic diagram of the device structure of the present invention; Figure 4 A schematic diagram of the preparation of the laser annealing P / N ohmic contact of the present invention; Figure 5 The XRD (X-ray diffraction) test results of the sample after annealing in Example 1 of the present invention; Figure 6 The test result of the source N-type ohmic contact in Example 1 of the present invention; Figure 7 The test results of the source P-type ohmic contact in Example 1 of the present invention; Figure 8 A flow chart for preparing the device of the present invention; Among them, 1 is the source N-type ion implantation area, 2 is the source P-type ion implantation area, 3 is the N-type epitaxial wafer, 4 is the gate oxide layer, 5 is the polysilicon gate, 6 is the source metal, 7 is the drain metal, 8 is the laser, and 9 is the SiC MOSFET. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0020] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0021] Example 1 This embodiment is a method for forming an ohmic contact when the source metal layer is a three-layer structure of Al / Ti / Ni / SiC. The process is as follows Figure 8 As shown, including: Step 1: Use a 350μm thick N-type 4H-SiC substrate with two epitaxial layers. The first layer is a 1μm buffer layer with a doping concentration of 1×10 18 cm -3 The second layer is a 10 μm N-type doped layer with a doping concentration of 5×10 15 cm -3 . Carry out RCA standard cleaning process; Step 2: Use ion implantation to implant nitrogen ions and aluminum ions to form N-type and P-type regions respectively. The doping concentration of N-type ions is 1×10 18 cm -3 , the P-type ion implantation concentration is 1×10 19 cm -3 , to obtain a sufficiently low specific contact resistance; the structure after epitaxy and ion implantation is as follows Figure 1 shown.

[0022] Step 3: Use rapid thermal annealing process at 1600℃ for 15min to repair the lattice and activate the doped ions; Step 4: preparing a gate oxide layer by dry oxidation and nitric oxide passivation; Step 5: Prepare a polysilicon gate by low pressure chemical vapor deposition; the structure of the gate oxide layer and the electrode after preparation is as follows Figure 2 As shown, Step 6: Deposit Ni 50nm, Ti 50nm, and Al 50nm on the source electrode in sequence by magnetron sputtering, and pattern them by photolithography and etching; Step 7: Thin the back of SiC to reduce the on-resistance, and deposit 100nm of Ni on the back drain by magnetron sputtering; Step 8: If Figure 4 As shown, a 248nm laser is used, which is shaped into a flat-top beam and emits 2.75J / cm 2 The source electrode was laser annealed at an energy density of 1.8 J / cm 2 The drain electrode is laser annealed, and the source and drain electrodes form ohmic contacts. The device structure is as follows: Figure 3 shown.

[0023] The XRD test results of the samples after annealing are as follows: Figure 5 As shown, it indicates that Si is generated at the interface.

[0024] The circular transmission line model (CTLM) was used to test the electrical properties of the samples and calculate the specific contact resistance. The specific contact resistance test results are shown in Figure 6 and Figure 7 The contact resistivity of the N-type and P-type ohmic contacts formed under this condition is 9.25×10 -6 Ω·cm 2 to 8.28×10 -7 Ω·cm 2 Compared with the RTP process, the specific contact resistivity of the P-type ohmic contact is reduced by 2 orders of magnitude while ensuring the specific contact resistivity of the N-type.

[0025] Example 2 This embodiment is a method for forming an ohmic contact when the source metal layer is a two-layer structure of Ti / Ni / SiC.

[0026] Step 1: Use an N-type 4H-SiC substrate with a thickness of 350 μm and two epitaxial layers on it. The first layer is a 1 μm buffer layer with a doping concentration of 1×10 18 cm -3 The second layer is a 25 μm N-type doped layer with a doping concentration of 5×10 15 cm -3 . Carry out RCA standard cleaning process; Step 2: Use ion implantation to implant nitrogen ions and aluminum ions to form N-type and P-type regions respectively. The doping concentration of N-type ions is 1×10 18 cm -3, the P-type ion implantation concentration is 1×10 19 cm -3 ; Step 3: Use rapid thermal annealing process at 1650°C for 15 minutes to repair the lattice and activate the doped ions; Step 4: preparing a gate oxide layer by dry oxidation and nitric oxide passivation; Step 5: preparing a polysilicon gate by a low pressure chemical vapor deposition method; Step 6: Deposit Ni 50nm and Ti 50nm on the source electrode in sequence by magnetron sputtering, and pattern them by photolithography and etching; Step 7: Thinning the substrate to 120 μm from the back side by a thinning process can reduce the on-resistance, and depositing 100 nm of Ni on the back drain by magnetron sputtering; Step 8: Use 532nm laser to shape into a flat top beam at 2.5J / cm 2 The source electrode was laser annealed at an energy density of 2.0 J / cm 2 The drain electrode is laser annealed to form ohmic contacts with the source and drain electrodes.

[0027] The circular transmission line model (CTLM) was used to test the electrical properties of the samples and calculate the specific contact resistance. The test results showed that the specific contact resistance of the N-type and P-type ohmic contacts formed under this condition was 2×10 -5 Ω·cm 2 to 5×10 -6 Ω·cm 2 Compared with the RTP process, the specific contact resistivity of the P-type ohmic contact is reduced by one order of magnitude while ensuring the specific contact resistivity of the N-type.

[0028] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a laser annealed silicon carbide ohmic contact, characterized in that: include: Performing RCA standard cleaning on an N-type 4H-SiC substrate, wherein two epitaxial layers are arranged on the N-type 4H-SiC substrate, namely a buffer layer and an N-type doping layer; Using ion implantation to form a P-type doping region and an N-type doping region in a 4H-SiC epitaxial layer, and performing rapid thermal annealing to obtain an epitaxial wafer; A metal layer is deposited on the P-type and N-type regions of the epitaxial wafer to form a source electrode, and high-energy laser annealing is performed on the source electrode region to form an ohmic contact.

2. The method for preparing a laser annealed silicon carbide ohmic contact according to claim 1, characterized in that: The thickness of the N-type doping layer is 10 μm-25 μm.

3. The method for preparing a laser annealed silicon carbide ohmic contact according to claim 1, characterized in that: The ions implanted by the ion implantation method are nitrogen ions and aluminum ions respectively.

4. The method for preparing a laser annealed silicon carbide ohmic contact according to claim 1, characterized in that: The temperature of the rapid thermal annealing is 1600°C-1650°C.

5. The method for preparing a laser annealed silicon carbide ohmic contact according to claim 1, characterized in that: The metal layer is an Al / Ti / Ni composite metal layer or a Ni / Ti composite metal layer.

6. The method for preparing a laser annealed silicon carbide ohmic contact according to claim 1, characterized in that: The laser annealing conditions are as follows: the laser wavelength is 248nm-532nm, the energy density is 2.5J / cm 2 -2.75J / cm 2 .

7. An ohmic contact formed by the method according to any one of claims 1 to 6.

8. A method for preparing a device, characterized in that: include: Performing RCA standard cleaning on an N-type 4H-SiC substrate, wherein two epitaxial layers are arranged on the N-type 4H-SiC substrate, namely a buffer layer and an N-type doping layer; Using ion implantation to form a P-type doping region and an N-type doping region in a 4H-SiC epitaxial layer, and performing rapid thermal annealing to obtain an epitaxial wafer; Preparing and patterning a gate oxide layer region above the epitaxial wafer; Depositing polysilicon or metal in the gate region for use as a gate electrode; Depositing a metal layer on the P-type and N-type regions of the epitaxial wafer to form a source electrode, and performing laser annealing on the source electrode region to form an ohmic contact; Metal Ni is deposited on the back of the epitaxial wafer to form a drain electrode, and laser annealing is performed on the drain electrode area to form an ohmic contact.

9. The method for preparing the device according to claim 8, characterized in that: The laser annealing conditions are as follows: the laser wavelength is 248nm-532nm, the energy density is 1.8J / cm 2 -2.75J / cm 2 .

10. A device prepared by the method of claim 8 or 9.

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