Method for laser annealing preparation of si c ohmic contact

Abstract

The application provides a method for preparing SiC ohmic contact by laser annealing. The method comprises the following steps: providing a SiC device structure to be processed, the SiC device structure comprising a SiC substrate layer and a surface metal layer for forming silicide; annealing the upper surface of the SiC device structure by using a combination of a first laser beam and a second laser beam, the first laser beam being used for preheating the SiC device structure, and the second laser beam being used for temperature control of the SiC device structure; wherein in the same pulse cycle, the pulse width of the first laser beam is smaller than the pulse width of the second laser beam, and after the first laser beam is loaded, a delay time is set, and the second laser beam starts to be loaded. By using the combination of the first laser beam and the second laser beam to anneal the SiC device structure, the annealing temperature and the annealing time can be accurately adjusted, so as to produce appropriate chemical products, and the SiC ohmic contact meeting the requirements can be obtained.

Description

Technical Field

[0001] This invention relates to the field of laser annealing technology, and in particular to a method for preparing SiC ohmic contacts by laser annealing. Background Technology

[0002] Silicon carbide (SiC) possesses properties such as wide bandgap, high breakdown field, high electron saturation drift velocity, and high thermal conductivity, making it a commonly used semiconductor material in high-temperature, high-power, and high-frequency devices. The performance of SiC devices under forward bias voltage is typically limited by their contact resistance; therefore, achieving low contact resistivity and ohmic characteristics is one of the key process challenges in fabricating high-performance SiC devices.

[0003] The formation of an ohmic contact between a metal and a semiconductor means that the contact point between the metal and the semiconductor can act as a pure resistor, and the smaller the resistance, the better. This allows most of the voltage to not be applied to the contact surface between the metal and the semiconductor during device operation, thereby improving device performance.

[0004] In the fabrication of SiC ohmic contacts, a metal layer (e.g., Ni and Nb) is typically deposited on a SiC substrate, and then the SiC substrate and the metal layer are annealed to form the SiC ohmic contact. Studies have found that Ni / 4H-SiC ohmic contacts require annealing at 900℃-1100℃ for 2-15 minutes to form. When preparing SiC ohmic contacts using Rapid Thermal Annealing (RTA) under nitrogen, annealing at 1000℃ for 2 minutes can form Ni / Nb / 4H-SiC ohmic contacts. The amount of Nb6C5 and Ni2Si compounds generated during annealing is a significant factor affecting the resistivity of the formed Ni / SiC ohmic contacts. For annealed Nb / 4H-SiC ohmic contacts, microstructure analysis after annealing revealed the formation of Nb2C and Nb3Si at annealing temperatures between 700℃ and 900℃, and Nb6C5 and Nb5Si3 at annealing temperatures of 1000℃. No carbon precipitation was observed in any sample. These results indicate that the resistivity of SiC ohmic contacts prepared by annealing is directly related to the annealing temperature and time. To obtain SiC ohmic contacts with low resistivity, a suitable high-temperature annealing process is required.

[0005] Traditional furnace annealing requires a long annealing time and affects the redistribution of implanted impurity ions in the device, while also leading to deterioration of electrode surface damage. Rapid thermal annealing, on the other hand, lacks precise control over the annealing range and temperature. In contrast, ohmic contacts prepared using pulsed laser irradiation annealing (LSA) technology offer significant advantages in terms of electrode surface morphology, interface morphology, and electrode layer composition uniformity, making it the preferred method for forming SiC ohmic contacts. The key to LSA technology lies in the flexible control of annealing temperature and time to ensure efficient interdiffusion and chemical reactions between the metal layer and the semiconductor substrate.

[0006] In recent years, the fabrication of SiC ohmic contacts using LSA technology has primarily employed single-pulse laser annealing of SiC devices. However, this method suffers from low activation efficiency, inability to effectively control the chemical reaction time between the metal layer and the SiC substrate, and failure to generate the desired chemical products. Consequently, the resistivity of the resulting SiC ohmic contacts falls short of expectations, thus hindering the performance improvement of SiC devices. Therefore, current LSA technology still requires improvement. Summary of the Invention

[0007] This invention provides a method for preparing SiC ohmic contacts by laser annealing, which can precisely control the annealing temperature and annealing time to generate suitable chemical products, so that the resistivity of the SiC ohmic contact reaches the desired value, thereby helping to improve the performance of SiC devices.

[0008] This invention provides a method for preparing SiC ohmic contacts by laser annealing, the method comprising:

[0009] A SiC device structure to be processed is provided, the SiC device structure including a SiC substrate layer and a surface metal layer for forming silicides;

[0010] The upper surface of the SiC device structure is annealed using a combination of a first laser beam and a second laser beam. The first laser beam is used to preheat the SiC device structure, and the second laser beam is used to control the temperature of the SiC device structure. Within the same pulse period, the pulse width of the first laser beam is smaller than the pulse width of the second laser beam, and after the first laser beam finishes loading, a set delay time is set before the second laser beam starts loading.

[0011] Optionally, the interface reaction between the surface metal layer and the SiC substrate layer occurs within a set temperature range, and during the preheating of the SiC device structure by the first laser beam, the temperature of the SiC device structure reaches at least the lower limit of the set temperature range.

[0012] Optionally, during the process of temperature control of the SiC device structure by the second laser beam, the temperature of the SiC device structure reaches at least the upper limit of the set temperature range.

[0013] Optionally, the set temperature range is 900℃~1100℃.

[0014] Optionally, the set delay time is 0ns to 100ns within a single pulse cycle.

[0015] Optionally, both the first laser beam and the second laser beam are ultraviolet pulsed lasers, and their wavelengths are both in the range of 244nm to 364nm.

[0016] Optionally, the pulse width of the first laser beam is less than or equal to 20 ns, and the pulse width of the second laser beam is 2 to 10 times the pulse width of the first laser beam.

[0017] Optionally, the energy density of the first laser beam is in the range of 0.4 J / cm². 2 ~0.8J / cm 2 The energy density of the second laser beam is in the range of 0.6 J / cm². 2 ~1.6J / cm 2 .

[0018] Optionally, the first laser beam and the second laser beam have the same pulse frequency.

[0019] Optionally, the pulse frequencies of the first laser beam and the second laser beam are 20kHz to 50kHz.

[0020] Optionally, during the laser annealing process, the temperature of the surface metal layer is controlled to be below the melting point of the surface metal layer material.

[0021] Optionally, the SiC substrate layer has a crystal form of 3C-SiC, 4H-SiC, or 6H-SiC.

[0022] Optionally, the material of the surface metal layer includes at least one of Ni, Ti, Co, Al, Nb, or Pt.

[0023] Optionally, the first laser beam and the second laser beam irradiate the surface metal layer to form a first light spot and a second light spot, respectively. During the scanning process, the first light spot and the second light spot move in the scanning direction, respectively. The overlap rate of two adjacent first light spots in the scanning direction is greater than 50% and less than 100%, and the overlap rate of two adjacent second light spots in the scanning direction is greater than 50% and less than 100%.

[0024] Optionally, the spatial energy distribution of either the first laser beam or the second laser beam is a Gaussian distribution or a super-Gaussian distribution.

[0025] In the laser annealing method for preparing SiC ohmic contacts of the present invention, a combination of a first laser beam and a second laser beam is used to anneal the upper surface of the SiC device structure. The first laser beam is used to preheat the SiC device structure, and the second laser beam is used to control the temperature of the SiC device structure. Within the same pulse period, the pulse width of the first laser beam is smaller than the pulse width of the second laser beam. After the first laser beam finishes loading, a set delay time is set before the second laser beam begins loading. Since the pulses of the first and second laser beams can be modulated separately and the set delay time between them can be adjusted, using their combination to perform laser annealing on the SiC device structure allows for more precise control of the annealing temperature and time. This ensures that the SiC device structure remains within the reaction temperature range for as long as possible to produce suitable chemical products, facilitating the acquisition of a SiC ohmic contact that meets the requirements. Attached Figure Description

[0026] Figure 1 This is a flowchart of a method for preparing SiC ohmic contacts by laser annealing according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a SiC device structure according to an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the time sequence of the first laser beam and the second laser beam within a single period in one embodiment of the present invention.

[0029] Figure 4 This is a schematic diagram of the light intensity distribution of the light spots formed by the first laser beam and the second laser beam in one embodiment of the present invention.

[0030] Figure 5 The graph shows the relationship between the energy density and the interface temperature of the SiC device structure obtained from the first simulation test.

[0031] Figure 6 The graph shows the relationship between energy density and reaction time obtained from the first simulation test.

[0032] Figure 7 The graph shows the relationship between the energy density obtained from the second simulation test and the interface temperature of the SiC device structure.

[0033] Figure 8 The graph shows the relationship between energy density and reaction time obtained from the second simulation test.

[0034] Figure 9This is a temperature field distribution diagram of each interface of the SiC device structure obtained from the third simulation test.

[0035] Figures 10 to 12 The temperature field distribution of the Nb / SiC interface obtained from the third simulation test is shown.

[0036] Figure 13 The graph shows the relationship between delay time and reaction time obtained from the third simulation test.

[0037] Figure 14 The temperature field distribution diagram of each interface of the SiC device structure was obtained from the fourth simulation test.

[0038] Figures 15 to 17 The temperature field distribution of the Nb / SiC interface obtained from the fourth simulation test is shown.

[0039] Figure 18 The graph shows the relationship between delay time and reaction time obtained from the fourth simulation test.

[0040] Figure 19 The graph shows the relationship between the maximum reaction time and the optimal process conditions for different pulse widths of the second laser beam, with the pulse width of the first laser beam fixed at 10 ns. Detailed Implementation

[0041] The method for preparing SiC ohmic contacts by laser annealing proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0042] Existing methods for preparing SiC ohmic contacts using laser annealing typically employ single-pulse lasers to anneal the SiC substrate and its surface metal layer. However, single-pulse laser annealing for SiC ohmic contacts suffers from limitations in effectively controlling the annealing temperature and time. This results in the inability to directionally generate the desired chemical products, and the poor uniformity of these products leads to the resistivity of the resulting SiC ohmic contacts failing to meet expectations. Consequently, the performance of SiC devices cannot be effectively improved, and the requirements cannot be satisfied.

[0043] To address the aforementioned problems, this invention provides a method for preparing SiC ohmic contacts using laser annealing. This method can be applied to the manufacturing process of SiC devices. Figure 1 This is a flowchart illustrating a method for preparing SiC ohmic contacts using laser annealing according to an embodiment of the present invention. Figure 1As shown, in one embodiment, the method for preparing SiC ohmic contacts by laser annealing includes a first step and a second step. In the first step, a SiC device structure to be processed is provided, the SiC device structure including a SiC substrate layer and a surface metal layer for forming silicide. In the second step, a combination of a first laser beam and a second laser beam is used to anneal the upper surface of the SiC device structure. The first laser beam is used to preheat the SiC device structure, and the second laser beam is used to control the temperature of the SiC device structure. Within the same pulse period, the pulse width of the first laser beam is less than the pulse width of the second laser beam, and after the first laser beam finishes loading, a set delay time is set before the second laser beam begins loading.

[0044] In this embodiment of the invention, the SiC ohmic contact to be prepared can be understood as such that the contact between the metal layer deposited on the SiC substrate and the SiC substrate is a pure resistor with a low resistivity. The method for preparing the SiC ohmic contact by laser annealing is to form the SiC ohmic contact by laser annealing the SiC device structure.

[0045] The method for preparing SiC ohmic contacts by laser annealing according to an embodiment of the present invention will be further described below. First, in the first step, a SiC device structure to be processed is provided. Figure 2 This is a schematic diagram of a SiC device structure according to an embodiment of the present invention. Figure 2 As shown, in one embodiment, the SiC device structure to be laser annealed includes a SiC substrate layer 10 and a surface metal layer 20 for forming silicides. An insulating layer 30 may be formed on the sides of the SiC substrate layer 10 and the surface metal layer 20.

[0046] Specifically, in the SiC substrate 10, the SiC crystal form can be 3C-SiC, 4H-SiC, or 6H-SiC. However, it is not limited to this; in other embodiments, SiC can also be other types of crystal structures. Here, 3C, 4H, and 3C represent different atomic stacking orders, C represents a cubic lattice structure, H represents a hexagonal lattice structure, and 3, 4, and 6 represent stacking cycle periods. 3C represents a cubic lattice structure formed by close-packed SiC atoms with a period of 3 layers, 4H represents a hexagonal lattice structure formed by close-packed atoms with a period of 4 layers, and 6H represents a hexagonal lattice structure formed by close-packed atoms with a period of 6 layers.

[0047] The material of the surface metal layer 20 formed on the surface of the SiC substrate 10 may include at least one of the metals used in SiC devices, such as Ni (nickel), Ti (titanium), Co (cobalt), Al (aluminum), Nb (niobium), or Pt (platinum). The metal layer may be a single-layer structure or a multilayer structure.

[0048] As an example, the SiC substrate 10 is, for example, 4H-SiC, and the surface metal layer 20 includes an Nb metal layer 21 covering the SiC substrate 10 and a Ni metal layer 22 covering the Nb metal layer. Along Figure 2 In the negative Y-axis direction, the thickness of the 4H-SiC substrate can be 350 μm, and the thickness of both the Nb and Ni metal layers can be 50 nm; the width of the 4H-SiC substrate, Nb metal layer, and Ni metal layer along the X-axis can all be 1 mm. The Nb and Ni metal layers can be formed by physical vapor deposition or atomic layer deposition.

[0049] In the second step described above, the upper surface of the surface metal layer 20 is annealed using a combination of a first laser beam and a second laser beam. The first laser beam is used to preheat the SiC device structure, and the second laser beam is used to control the temperature of the SiC device structure. Within the same pulse period, the pulse width of the first laser beam is less than the pulse width of the second laser beam, and after the first laser beam finishes loading, a set delay time is set before the second laser beam starts loading.

[0050] Specifically, the interfacial reaction between the surface metal layer and the SiC substrate layer can occur within a set temperature range. For example, the set temperature range is 900℃ to 1100℃.

[0051] During the process of preheating the SiC device structure by the first laser beam, the temperature of the SiC device structure can reach at least the lower limit of the set temperature range, for example, at least 900°C, so that the second laser beam can subsequently control the temperature of the SiC device structure.

[0052] During the process of temperature control of the SiC device structure by the second laser beam, the temperature of the SiC device structure can reach at least the upper limit of the set temperature range (i.e., at least not lower than the upper limit of the set temperature range), for example, at least 1100°C. This allows the temperature of the SiC device structure to be within the temperature range of the interface reaction (i.e., within the reaction temperature range), which helps to form a SiC ohmic contact that meets the requirements.

[0053] The pulse width of the first laser beam can be less than or equal to 20 ns, and the pulse width of the second laser beam can be 2 to 10 times the pulse width of the first laser beam. However, it is not limited to this, and those skilled in the art can adjust the pulse widths of the first and second laser beams according to actual needs.

[0054] The energy density of the first laser beam can be in the range of 0.4 J / cm². 2 ~0.8J / cm2 The energy density range of the second laser beam can be 0.6 J / cm². 2 ~1.6J / cm 2 .

[0055] The first laser beam and the second laser beam irradiate the surface metal layer, forming a first light spot and a second light spot, respectively. Within the same pulse cycle, the formation positions of the first light spot and the second light spot can be the same; that is, within the same pulse cycle, the first laser beam and the second laser beam can irradiate the same position on the upper surface of the surface metal layer, jointly performing laser annealing on the SiC device structure. The shape and size of the first light spot and the second light spot can be the same.

[0056] During the scanning process, the first light spot and the second light spot move in the scanning direction respectively. The overlap rate of two adjacent first light spots in the scanning direction can be greater than 50% and less than 100%, and the overlap rate of two adjacent second light spots in the scanning direction can be greater than 50% and less than 100%.

[0057] The first laser beam and the second laser beam can have the same pulse frequency to maintain synchronization in the pulse period time sequence. The first laser beam and the second laser beam can be generated by different lasers, allowing for independent adjustment. Optionally, the pulse frequencies of the first laser beam and the second laser beam can be set in the range of 20kHz to 50kHz.

[0058] Figure 3 This is a schematic diagram illustrating the time series of the first and second laser beams within a single period in one embodiment of the present invention. Figure 3 As shown, in one embodiment, within a single pulse cycle (referring to the pulse cycle of laser annealing), the first laser beam and the second laser beam maintain synchronization in the pulse cycle time sequence. After the pulse loading of the first laser beam ends, a set delay time is set, and the pulse loading of the second laser beam begins. The pulse width (duration) of the first laser beam is less than the pulse width of the second laser beam. The pulse delay between the first laser beam and the second laser beam can be controlled by the delay controller of the laser annealing device.

[0059] By setting an appropriate delay time between the pulses of the first and second laser beams—that is, the first laser beam preheats the SiC device structure, and the second laser beam begins loading when the SiC device structure is at a certain temperature—the annealing temperature and time can be effectively controlled. In particular, the interface reaction temperature and time between the SiC substrate and the metal layer can be effectively controlled, which helps to generate suitable chemical products and improve the performance of the SiC device. Optionally, within a single pulse cycle, the set delay time from the end of the first laser beam's pulse loading to the start of the second laser beam's pulse loading can be 0 ns to 100 ns. In one embodiment, the set delay time range can be 0 ns to 10 ns or 0 ns to 20 ns.

[0060] Since lasers that generate wavelengths below 244nm (short-wavelength lasers) are more expensive than lasers that generate wavelengths between 244nm and 364nm (long-wavelength lasers), in order to reduce the cost of laser annealing for preparing SiC ohmic contacts, both the first and second laser beams can be ultraviolet pulsed lasers, and both can have wavelengths in the range of 244nm to 364nm. For example, the wavelengths of both the first and second laser beams are 355nm.

[0061] The spatial energy distribution of either the first laser beam or the second laser beam can be a Gaussian distribution or a super-Gaussian distribution. Figure 4 This is a schematic diagram of the light intensity distribution of the light spot formed by focusing the first laser beam and the second laser beam in one embodiment of the present invention. Figure 4 As shown, when the spatial energy distribution of the first laser beam and the second laser beam is Gaussian, the light intensity of the light spots formed by the first laser beam and the second laser beam conforms to the relationship (1):

[0062]

[0063] In relation (1), I G r is the center peak intensity of the laser beam. G Let r be the beam radius, and r be the distance from any point on the beam spot to the center of the beam spot.

[0064] When the spatial energy distribution of the first laser beam and the second laser beam is a super-Gaussian distribution, the light intensity of the light spots formed by the first laser beam and the second laser beam conforms to the relationship (2):

[0065]

[0066] In relation (2), I s r is the center peak energy of the laser beam. sLet r be the beam radius, r be the distance from any point on the spot to the center of the spot, and n be the order of the super-Gaussian beam (n is an integer and greater than 2). When the spatial energy distribution of the first laser beam and the second laser beam is a super-Gaussian distribution, the higher the order of the super-Gaussian beam, the more uniform the energy of the formed spot, that is, the larger the flat-top range on the spot energy distribution curve.

[0067] When a 12th-order super-Gaussian laser beam irradiates the upper surface of a surface metal layer, the transmittance of the laser beam can be approximated as zero. Part of the laser energy is reflected by the metal surface, and the remaining unreflected energy is absorbed along the depth of the material (metal layer and SiC substrate layer) according to Lambert's law. The light intensity exhibits exponential decay along the depth of the material. Figure 2 Taking the SiC device structure shown as an example, in the negative Y-axis direction, the vertical distance from each point in the SiC device structure to the upper surface of the surface metal layer is y. Within the laser beam irradiation range, the light intensity obtained at each point in the SiC device structure conforms to the relationship (3):

[0068] I=αI0e -αy (3)

[0069] In equation (3), I0 is the original light intensity and α is the absorption coefficient of the material to the laser energy.

[0070] The light energy absorbed in the depth direction of the material will be absorbed by electrons, causing electrons to undergo energy level transitions. After gaining kinetic energy, the transitioned electrons collide with the crystal lattice, thereby increasing the temperature of the entire device. The heat conduction process inside the device follows Fourier's law of thermal conduction, that is, it satisfies the relationship (4):

[0071]

[0072] In equation (4), the energy of the light field absorbed by the material is Q(y,t)=(1-R)αI0e -αy R is the reflectivity of the material surface. ρ(T) is the density of the material, Cp(T) is the specific heat capacity, and D(T) is the thermal diffusivity. ρ(T), Cp(T), and D(T) are all functions of temperature T.

[0073] Research has found that during laser annealing of SiC device structures, a chemical reaction occurs at the interface between the SiC substrate and the metal Nb, producing Nb. x Si x and Nb x C x The reaction temperature for the chemical products is in the range of 900℃ to 1100℃. In this embodiment, the reaction temperature range for the formation of the SiC ohmic contact in the SiC device structure can be set to 900℃ to 1100℃.

[0074] In this embodiment, the reaction time of the SiC device structure can be defined as the time for laser (e.g., pulsed laser) loading or cooling when the temperature of the SiC device structure is within the temperature range of 900℃ to 1100℃. Specifically, the pulse loading time of the first laser beam and the second laser beam is the aforementioned laser loading time; after the pulse loading of the first laser beam ends, a set delay time is set before the pulse loading of the second laser beam begins. During the delay phase, the temperature of the SiC will decrease, and the aforementioned cooling time is the delay time. In other words, the reaction time of the SiC device structure (which can be simply referred to as "reaction time") can be the time it takes for its temperature to be within the range of 900℃ to 1100℃.

[0075] To ensure that the entire annealing process occurs below the melting point of the surface metal layer material (i.e., the annealing temperature is controlled below the melting point of the metal layer material) and to obtain a relatively perfect annealing process window with a combination of long and short pulse widths (the combination of the first laser beam and the second laser beam), the inventors conducted simulation tests on the laser annealing preparation of SiC ohmic contacts under different conditions. The specific test conditions are shown below.

[0076] The conditions for the first simulation test were: a single-pulse laser beam with a pulse width of 10 ns was used.

[0077] The conditions for the second simulation test are: a single-pulse laser beam with a pulse width of 50 ns is used.

[0078] The conditions for the third simulation test are as follows: a combination of the first laser beam and the second laser beam is used, with the pulse width of the first laser beam being 10ns and the pulse width of the second laser beam being 30ns.

[0079] The conditions for the fourth simulation test are as follows: a combination of the first laser beam and the second laser beam is used, with the pulse width of the first laser beam being 10 ns and the pulse width of the second laser beam being 50 ns.

[0080] The simulation tests under the above four conditions all utilize a 355nm wavelength laser beam to examine the SiC device structure (e.g., Figure 2 The SiC device structure shown is subjected to laser annealing. The overlap rate of the laser beam spot formed on the surface of the SiC device structure in the scanning direction can be 66.7%, and the scanning speed of the spot can be 1m / s.

[0081] The simulation test results for the above four conditions are explained below.

[0082] <First-Condition Simulation Test>

[0083] Figure 5 The graph shows the relationship between the energy density and the interface temperature of the SiC device structure obtained from the first simulation test. Figure 6 The graph shows the relationship between energy density and reaction time obtained from the first simulation test.

[0084] The results of the first simulation test are as follows: Figure 5 and Figure 6 As shown, the melting point energy density threshold of the Ni metal layer surface is approximately 0.8 J / cm². 2 Below the melting point energy density threshold of the Ni metal layer surface, the reaction time of the SiC device structure is up to about 5 ns; above the melting point energy density threshold of the Ni metal layer surface, the reaction time is up to about 8 ns.

[0085] <Second Condition Simulation Test>

[0086] Figure 7 The graph shows the relationship between the energy density obtained from the second simulation test and the interface temperature of the SiC device structure. Figure 8 The graph shows the relationship between energy density and reaction time obtained from the second simulation test.

[0087] The results of the second simulation test are as follows: Figure 7 and Figure 8 As shown, the melting point energy density threshold of the Ni metal layer surface is approximately 1.8 J / cm². 2 When the reaction time is below the melting point energy density threshold of the Ni metal layer surface, the maximum reaction time is approximately 20 ns; when the reaction time is above the melting point energy density threshold of the Ni metal layer surface, the maximum reaction time is approximately 22 ns.

[0088] <Third Condition Simulation Test>

[0089] The third simulation test involved laser annealing of the SiC device structure using a combination of a first laser beam with a pulse width of 10 ns and a second laser beam with a pulse width of 30 ns. Within one pulse cycle, the first laser beam was initially applied to preheat the SiC device structure. After a set delay interval, the second laser beam was applied to control the temperature of the SiC device structure. During the laser annealing process, the surface temperature of the surface metal layer was controlled below the melting point of the metal layer material, ensuring that the surface of the annealed surface metal layer remained intact (without high-temperature damage). This resulted in a better surface morphology of the formed SiC ohmic contact electrodes, contributing to improved performance of the SiC device.

[0090] According to the results of the first simulation test, the melting point energy density threshold of the Ni metal layer surface is approximately 0.8 J / cm². 2 Because the SiC device structure needs to be laser annealed below the melting point of the surface metal layer material, the energy density of the first laser beam can be controlled to be less than or equal to 0.8 J / cm². 2 Within the range. In the third simulation test, the energy density of the second laser beam was selected and controlled to be less than or equal to 1.2 J / cm². 2Within a certain range, laser annealing is performed on the SiC device structure below the melting point of the surface metal layer material.

[0091] After the pulse loading (preheating stage) of the first laser beam ends, a delay stage without laser loading begins. In this simulation test, the delay time is tested within the range of 0ns to 20ns. After the delay stage ends, the pulse loading (temperature control stage) of the second laser beam begins. The energy density of the second laser beam can be selected at 0.8J / cm². 2 ~1.2J / cm 2 Within the specified range, tests showed that under these conditions, the temperature of the surface metal layer was below its melting point, and the SiC device structure remained in the reaction temperature region for a relatively long time.

[0092] Figure 9 This is a temperature field distribution diagram of each interface of the SiC device structure obtained from the third simulation test. Figures 10 to 12 This is a temperature field distribution diagram of the Nb / SiC interface obtained from the third simulation test. In the temperature field distribution diagram, the horizontal axis represents the annealing time, and the vertical axis represents the interface temperature. Figure 9 In the first laser beam, the energy density is 0.8 J / cm². 2 The energy density of the second laser beam is 1.0 J / cm². 2 The delay time between the pulses of the first laser beam and the second laser beam is 0 ns. Figures 10 to 12 In this process, the energy density of the first laser beam used is 0.8 J / cm². 2 The delay times between the first and second laser beam pulses are 0ns, 5ns, and 10ns, respectively. The difference is that... Figure 10 The energy density of the second laser beam is 0.8 J / cm². 2 , Figure 11 The energy density of the second laser beam is 1.0 J / cm². 2 , Figure 12 The energy density of the second laser beam is 1.2 J / cm². 2 .

[0093] As can be seen from the third simulation test, Figures 9 to 12 As shown, the length of the delay time mainly affects the starting point of the pulse loading time of the second laser beam. Changes in the delay time will lead to a larger temperature range corresponding to the loading stage of the second laser beam. Moreover, the longer the delay time, the lower the Nb / SiC interface temperature corresponding to the starting point of the pulse loading time of the second laser beam. However, it has little impact on the highest temperature value of the Nb / SiC interface during the pulse loading stage of the second laser beam.

[0094] Figure 13 The graph shows the relationship between delay time and reaction time obtained from the third simulation test. Figure 13In the first laser beam, the energy density is 0.8 J / cm². 2 The energy density of the second laser beam is 0.8 J / cm². 2 1.0 J / cm 2 and 1.2J / cm 2 .like Figure 13 As shown, with a delay time of 0 ns, the energy density of the second laser beam is 0.8 J / cm². 2 At that time, the reaction time corresponding to the SiC device structure was 21 ns; the energy density of the second laser beam was 1.0 J / cm². 2 At that time, the response time corresponding to the SiC device structure was 29 ns; the energy density of the second laser beam was 1.2 J / cm². 2 At that time, the response time of the SiC device structure was 22 ns. With increasing delay time, the response time of the SiC device structure tended to decrease. The energy density of the first laser beam was 0.8 J / cm². 2 The energy density of the second laser beam is 1.0 J / cm². 2 When the delay time of the first laser beam and the second laser beam is 0 ns, the reaction time of the SiC device structure is the longest.

[0095] The third simulation test also revealed that the energy density of the first laser beam can reach 0.4 J / cm². 2 ~0.8J / cm 2 The energy density range of the second laser beam can be 0.6 J / cm². 2 ~1.2J / cm 2 The delay time between the first laser beam and the second laser beam can be 0ns to 20ns. Under the above annealing conditions (process window), the laser annealing process occurs below the melting point of the metal layer material, which can also effectively control the reaction time of the SiC device structure, thereby producing the required chemical products with good uniformity, which helps to obtain SiC ohmic contacts with low resistivity.

[0096] <Fourth Condition Simulation Test>

[0097] The fourth simulation test involves laser annealing of the SiC device structure using a combination of a first laser beam with a pulse width of 10 ns and a second laser beam with a pulse width of 50 ns.

[0098] Figure 14 The temperature field distribution diagrams of each interface of the SiC device structure were obtained from the fourth simulation test. Figures 15 to 17 The temperature field distribution of the Nb / SiC interface obtained from the fourth simulation test is shown. Figure 14 The energy density of the first laser beam is 0.8 J / cm². 2The energy density of the second laser beam is 1.2 J / cm². 2 The delay time between the pulses of the first laser beam and the second laser beam is 0 ns. Figures 15 to 17 In this process, the energy density of the first laser beam used is 0.8 J / cm². 2 The delay times between the first and second laser beam pulses are 0ns, 5ns, and 10ns, respectively. The difference is that... Figure 15 The energy density of the second laser beam is 1.0 J / cm². 2 , Figure 16 The energy density of the second laser beam is 1.2 J / cm². 2 , Figure 17 The energy density of the second laser beam is 1.4 J / cm². 2 .

[0099] As can be seen from the fourth simulation test, Figures 14 to 17 As shown, the length of the delay time mainly affects the starting point of the second laser beam's pulse loading time. Changes in the delay time lead to a larger temperature range corresponding to the second laser beam loading stage. Moreover, the longer the delay time, the lower the Nb / SiC interface temperature corresponding to the starting point of the second laser beam's pulse loading time. However, it has little impact on the highest temperature value of the Nb / SiC interface during the second laser beam pulse loading stage. This is consistent with the results of the third simulation test.

[0100] Figure 18 The graph shows the relationship between delay time and reaction time obtained from the fourth simulation test. Figure 18 In the first laser beam, the energy density is 0.8 J / cm². 2 The energy density of the second laser beam is 1.0 J / cm². 2 1.2J / cm 2 and 1.4J / cm 2 .like Figure 18 As shown, with a delay time of 0 ns, the energy density of the second laser beam is 1.0 J / cm². 2 At that time, the response time corresponding to the SiC device structure was 16 ns; the energy density of the second laser beam was 1.2 J / cm². 2 At that time, the response time corresponding to the SiC device structure was 38 ns; the energy density of the second laser beam was 1.4 J / cm². 2 At that time, the response time of the SiC device structure was 36 ns. With increasing delay time, the response time of the SiC device structure tended to decrease. The energy density of the first laser beam was 0.8 J / cm². 2 The energy density of the second laser beam is 1.2 J / cm². 2 When the delay time of the first laser beam and the second laser beam is 0 ns, the reaction time of the SiC device structure is the longest.

[0101] The fourth simulation test also revealed that the energy density of the first laser beam can reach 0.4 J / cm². 2 ~0.8J / cm 2 The energy density of the second laser beam can be in the range of 0.8 J / cm². 2 ~1.6J / cm 2 The delay time between the first laser beam and the second laser beam can be 0ns to 20ns. Under the above annealing conditions (process window), the laser annealing process occurs below the melting point of the metal layer material, which can also effectively control the reaction time of the SiC device structure, thereby producing the required chemical products with good uniformity, which helps to obtain SiC ohmic contacts with low resistivity.

[0102] Comparing the results of the third and fourth simulation tests, it can be seen that when the delay time between the first and second laser beams is 0 ns, the response times obtained in the third simulation test are 21 ns, 29 ns, and 22 ns, respectively, while the response times obtained in the fourth simulation test are 16 ns, 38 ns, and 36 ns. That is, under the conditions of the fourth simulation test, the response time of the SiC device structure can be significantly increased. In other words, with the same delay time, appropriately increasing the pulse width of the second laser beam and selecting a suitable energy density can increase the response time.

[0103] Figure 19 With the pulse width of the first laser beam fixed at 10 ns, this study provides the relationship between reaction time and pulse width under optimal process conditions by varying the pulse width of the second laser beam. The optimal process conditions are defined as follows: both delays are 0 ns, the energy density of the first laser beam is controlled below the melting threshold (i.e., melting point) of the surface metal layer, and the energy density of the second laser beam is set to the value corresponding to maximizing the reaction time. Statistical results show that the reaction time is linearly correlated with the pulse width of the second laser beam; the longer the pulse width, the longer the reaction time.

[0104] A comparison of the results of the four simulation tests shows that, compared with the annealing method using a single-source, single-pulse laser, when using a dual-source, long-short-pulse laser combination (a combination of a first laser beam and a second laser beam with different pulse widths generated by different lasers) to perform laser annealing on SiC device structures, the first laser beam with a shorter pulse width preheats the SiC device structure first, and the second laser beam then controls the temperature of the SiC device structure. Therefore, appropriately reducing the energy density of the first and second laser beams can also enable the SiC device structure to reach the annealing temperature, thereby increasing the size of the spot formed by the first and second laser beams to improve the efficiency of laser annealing.

[0105] Since the first and second laser beams can be generated by different lasers, the laser adjustment is highly flexible. By selecting a suitable combination of pulse width and energy density and appropriately adjusting the set delay time between the first and second laser beams, the reaction time can be significantly increased. This reduces the overlap between the laser scanning direction and the stepping direction, thereby improving production efficiency. It also allows control over the reaction time and annealing temperature of the SiC device structure (especially the annealing temperature of each interface within the SiC device structure). Consequently, it allows control over the interface reaction to generate suitable chemical products with relatively good uniformity. At the same time, the temperature of the metal layer surface can be controlled below the melting point of the metal layer material, ensuring a good surface morphology and resulting in relatively low resistivity of the formed SiC ohmic contact, thus improving the performance of the SiC device.

[0106] In summary, in the laser annealing method for preparing SiC ohmic contacts in this embodiment, a combination of a first laser beam and a second laser beam is used to anneal the upper surface of the SiC device structure. The first laser beam is used to preheat the SiC device structure, and the second laser beam is used to control the temperature of the SiC device structure. Within the same pulse period, the pulse width of the first laser beam is less than the pulse width of the second laser beam, and after the first laser beam finishes loading, a set delay time is set before the second laser beam begins loading. Within the same pulse cycle, a first laser beam with a smaller pulse width can be used to preheat the SiC device structure to a certain temperature. Then, a second laser beam with a wider pulse width is used to control the temperature of the SiC device structure. The two laser beam pulses can be modulated separately, and the set delay time between them can be adjusted. By combining them to perform laser annealing on the SiC device structure, the annealing temperature and annealing time can be controlled more precisely, ensuring that the temperature of the upper surface of the metal layer does not exceed the melting point of the metal layer material, thus maintaining the integrity of the metal layer surface. At the same time, the reaction time of the chemical reaction at the interface between the SiC substrate and the metal layer can be controlled more precisely to produce suitable chemical products. Furthermore, when the annealing temperature is stably controlled, the uniformity of the chemical products generated at each laser annealing point within the annealing range is relatively good, which helps to achieve the desired resistivity of the SiC ohmic contact, thereby improving the performance of the SiC device.

[0107] It should be noted that, unless otherwise specified or indicated, the terms "first," "second," "third," etc., in the specification are used only to distinguish the various components, elements, and steps in the specification, and are not used to indicate the logical or sequential relationships between the various components, elements, and steps.

[0108] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing SiC ohmic contacts by laser annealing, characterized in that, include: A SiC device structure to be processed is provided, the SiC device structure including a SiC substrate layer and a surface metal layer for forming silicides; The upper surface of the SiC device structure is annealed using a combination of a first laser beam and a second laser beam. The first laser beam is used to preheat the SiC device structure, and the second laser beam is used to control the temperature of the SiC device structure. Within the same pulse period, the pulse width of the first laser beam is smaller than the pulse width of the second laser beam, and after the first laser beam finishes loading, a set delay time is set before the second laser beam starts loading. The interface reaction between the surface metal layer and the SiC substrate layer occurs within a set temperature range of 900°C to 1100°C. During the preheating of the SiC device structure by the first laser beam, the temperature of the SiC device structure reaches at least the lower limit of the set temperature range.

2. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, During the process of temperature control of the SiC device structure by the second laser beam, the temperature of the SiC device structure reaches at least the upper limit of the set temperature range.

3. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The set delay time is 0ns to 100ns.

4. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, Both the first laser beam and the second laser beam are ultraviolet pulsed lasers, and their wavelengths are both in the range of 244nm to 364nm.

5. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The pulse width of the first laser beam is less than or equal to 20 ns, and the pulse width of the second laser beam is 2 to 10 times the pulse width of the first laser beam.

6. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The energy density of the first laser beam is in the range of 0.4 J / cm². 2 ~0.8J / cm 2 The energy density of the second laser beam is in the range of 0.6 J / cm². 2 ~1.6J / cm 2 .

7. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The first laser beam and the second laser beam have the same pulse frequency.

8. The method for preparing SiC ohmic contacts by laser annealing as described in claim 7, characterized in that, The pulse frequencies of the first laser beam and the second laser beam are 20kHz to 50kHz.

9. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, During the annealing process, the temperature of the surface metal layer is controlled to be below the melting point of the surface metal layer material.

10. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The SiC substrate has a crystal form of 3C-SiC, 4H-SiC, or 6H-SiC.

11. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The material of the surface metal layer includes at least one of Ni, Ti, Co, Al, Nb, or Pt.

12. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The first laser beam and the second laser beam irradiate the surface metal layer to form a first light spot and a second light spot, respectively. During the scanning process, the first light spot and the second light spot move in the scanning direction, respectively. The overlap rate of two adjacent first light spots in the scanning direction is greater than 50% and less than 100%, and the overlap rate of two adjacent second light spots in the scanning direction is greater than 50% and less than 100%.

13. The method for preparing SiC ohmic contacts by laser annealing as described in claim 1, characterized in that, The spatial energy distribution of either the first laser beam or the second laser beam is a Gaussian distribution or a super-Gaussian distribution.

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