High thermal conductivity and strong bonding IGBT back-gold gradient composite coating and its preparation method

Abstract

This invention discloses a high thermal conductivity, strong bonding gradient composite coating for IGBT back-side metallization, comprising a Ti metal adhesion layer, a NiV metal barrier layer, and an Ag anti-oxidation, high thermal conductivity layer deposited sequentially from the inside out on an n-type Si substrate. The invention also discloses a method for preparing the composite coating, which involves first ion bombarding the substrate for cleaning, and then sequentially depositing the Ti metal adhesion layer, NiV metal barrier layer, and Ag anti-oxidation, high thermal conductivity coating on the substrate surface. Each deposition process includes two stages: low-power weak ionization and high-power strong ionization. The substrate is subjected to high-temperature heating treatment before the deposition of the Ag anti-oxidation, high thermal conductivity layer. The gradient composite coating of this invention exhibits excellent thermal conductivity and film-substrate bonding strength, while also possessing good hardness and metal barrier capability. The preparation method of this invention features high deposition efficiency, low internal stress and high bonding strength between the prepared heterogeneous coatings, and high surface quality.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor power device metallization fabrication technology, and relates to a high thermal conductivity and strong bonding IGBT back gold gradient composite coating. This invention also relates to a method for preparing the coating, which is particularly suitable for the preparation of the back gold layer of high-reliability IGBT chips under high voltage and high current scenarios. Background Technology

[0002] Insulated-gate bipolar transistors (IGBTs), as core power devices in the field of power electronics, are composite semiconductors that control output current through input voltage. They combine the advantages of high input impedance of MOSFETs and low on-state voltage drop of bipolar transistors, making them indispensable in high-voltage, high-current scenarios such as new energy vehicles, smart grids, rail transit, and industrial power conversion. Their performance directly determines the conversion efficiency, operational stability, and lifespan of power electronic devices. The gold-plated back coating of IGBTs, as a key connection layer between the chip and the external packaging and heat dissipation structure, must simultaneously meet four core performance requirements: high thermal conductivity (rapidly dissipating the large amount of Joule heat generated during chip operation to avoid local overheating failure), strong interfacial adhesion (resisting thermal and mechanical stresses caused by temperature cycling and mechanical vibration to prevent coating peeling and delamination), excellent diffusion barrier properties (inhibiting the increase in contact resistance caused by metal atom interdiffusion), and good solderability (ensuring the reliability of package soldering). It is a key core structure for improving the power density and long-term reliability of IGBT devices.

[0003] Currently, IGBT back-gold coatings generally employ a multi-layer composite structure of "adhesion layer - barrier layer - conductive solder layer / anti-oxidation and thermally conductive layer," with mainstream systems including Ti / Ni / Ag and Al / Ti / Ni / Ag. The Ti layer acts as an adhesion layer to improve adhesion to the silicon substrate, the intermediate layer acts as a diffusion barrier, and the surface Ag layer ensures solderability, conductivity, oxidation resistance, and thermal conductivity. However, existing technologies have some bottlenecks in practical applications, making it difficult to meet the performance requirements of next-generation high-power-density IGBTs. Specific shortcomings are as follows:

[0004] (1) Insufficient thermal conductivity and high interfacial thermal resistance. Traditional back-gold coatings often use pure Ni or ordinary Ni alloys as the intermediate barrier layer, which has low thermal conductivity and poor interfacial compatibility with Ti adhesion layer and Ag surface layer, easily forming a high-resistance interfacial layer, resulting in poor overall heat conduction path; at the same time, some processes use Al as the ohmic contact layer, which is prone to forming Al-Si alloy phase with silicon substrate at high temperature, further increasing interfacial thermal resistance and contact resistance, which cannot meet the high-efficiency heat dissipation requirements of high-power IGBTs, and is even more worrying in high-voltage and high-current scenarios.

[0005] (2) Poor coating bonding strength, prone to delamination failure. In the existing Ti-Ni-Ag system, the Ni layer is easily oxidized during high-temperature annealing (above 350℃) or long-term service, which leads to a sharp decrease in the adhesion between Ni and Ag layers and causes Ag layer to fall off; and the Ti layer and silicon substrate interface only form amorphous Ti-Si phase during low-temperature annealing (<500℃), with weak interface bonding. Although high-temperature annealing can form Ti silicide to improve bonding, it will damage the electrical performance of the active area on the front side of the IGBT, resulting in the deterioration of the overall reliability of the device; at the same time, the surface of the IGBT wafer is rough and damaged after back-side thinning, which further aggravates the bonding defects between the coating and the substrate, and delamination is prone to occur during power cycling.

[0006] (3) The interdiffusion suppression effect of metal atoms is not good, and the device life is shortened. The pure Ni barrier layer has a poor effect on blocking the interdiffusion of Ti and Ag atoms with silicon substrate. Under long-term high temperature conditions, it is easy to form brittle intermetallic compounds, which leads to coating cracking and increased contact resistance.

[0007] (4) Existing fabrication processes mostly use DC magnetron sputtering, which has problems such as low deposition efficiency, low interfacial bonding strength, and high internal stress. DC magnetron sputtering is in the glow discharge range with low gas discharge power density. The off-target mechanism of the cascade collision of coating particles leads to a low ionization rate, resulting in low deposition efficiency, low interfacial bonding strength, and high internal stress of the coating. It is difficult to meet the needs of large-scale mass production and the increasingly stringent performance requirements of device use standards.

[0008] To address the aforementioned issues, the industry urgently needs to optimize the layered structure and preparation process of the back gold coating. By rationally designing the material ratio and deposition parameters of each layer, it is possible to ensure the coating's high thermal conductivity and solderability while strengthening the interfacial bonding force and improving the atomic diffusion barrier capability, while also taking into account the simplicity of the process and mass production compatibility. Summary of the Invention

[0009] The purpose of this invention is to provide a high thermal conductivity and strong bonding IGBT back-gold gradient composite coating, which is a Ti / NiV / Ag coating, and has excellent thermal conductivity and film-substrate interface bonding strength.

[0010] Another objective of this invention is to provide a method for preparing the above-mentioned gradient composite coating, which has the advantage of high deposition efficiency, and the prepared heterogeneous coatings have the characteristics of low internal stress, high bonding force, excellent thermal conductivity and high surface quality.

[0011] The technical solution adopted in this invention is a high thermal conductivity and strong bonding IGBT back-gold gradient composite coating, which includes a Ti metal adhesion layer, a NiV metal barrier layer and an Ag anti-oxidation and high thermal conductivity layer deposited sequentially from the inside to the outside on the surface of an n-type Si substrate.

[0012] The invention is further characterized by: The thickness of the Ti metal adhesion layer is 100nm~300nm, the thickness of the NiV metal barrier layer is 400nm~500nm, and the thickness of the Ag anti-oxidation and high thermal conductivity layer is 600nm~1500nm; the gradient composite coating is composed of uniform and dense nanocrystals with a grain size of less than 50nm.

[0013] Another technical solution adopted in this invention is: The preparation method of the high thermal conductivity and strong bonding IGBT back-gold gradient composite coating is as follows: Step 1: Under vacuum conditions, argon gas is introduced, and the n-type Si substrate is cleaned by ion bombardment using a Ti target. Step 2: Turn on the Ti target sputtering mode and deposit a Ti metal adhesion layer on the substrate surface by controlling the two discharge stages of weak ionization and strong ionization. Step 3: Turn off the Ti target and turn on the NiV alloy target. By controlling the two discharge stages of weak and strong ionization, deposit a NiV metal barrier layer on the Ti metal adhesion layer. Step 4: Turn off the NiV target and heat the substrate; Step 5: Turn on the Ag target and deposit an Ag anti-oxidation and high thermal conductivity layer on the NiV metal barrier layer by controlling the two discharge stages of weak and strong ionization.

[0014] Another feature of the technical solution of this invention is that: In step 1, the vacuum degree is 2.5 × 10⁻⁶. -5 ~3.0×10 -5 Torr, argon flow rate 40~50mL / min, metal Ti target current DC 1.5~2.0A, cleaning time 5~8min.

[0015] In step 2, the peak voltages for the weak ionization and strong ionization stages are 200~250V and 600~700V, respectively; the pulse on-widths are 4~8ms and 8~10ms, respectively; the pulse off-width is 10~12ms; the argon flow rate is 40~60mL / min; the negative bias voltage is -60~-40V; the frequency is 50~60Hz; and the deposition time is 5~10min.

[0016] In step 3, the peak voltages for the weak ionization and strong ionization stages are 200~300V and 650~800V, respectively; the pulse on-widths are 4~8ms and 8~10ms, respectively; the pulse off-width is 10~12ms; the argon flow rate is 40~50mL / min; the frequency is 50~60Hz; the negative bias is -65~-50V; and the deposition time is 10~15min.

[0017] In step 4, the heating temperature is 400~450℃ and the heating time is 8~10min.

[0018] In step 5, the peak voltages for the weak ionization and strong ionization stages are 200~300V and 650~800V, respectively; the pulse on-widths are 4~8ms and 8~10ms, respectively; the pulse off-width is 10~12ms; the argon flow rate is 50~60mL / min; the negative bias voltage is -65~-50V; the frequency is 50~60Hz; and the deposition time is 20~50min.

[0019] The beneficial effects of this invention are: (1) The back gold coating of the IGBT of the present invention is a Ti-NiV-Ag gradient composite structure. The NiV alloy replaces the traditional pure Ni as the intermediate barrier layer, which has the following three advantages: First, the V element in the NiV alloy can effectively suppress the excessive growth of intermetallic compounds (such as Ni-Si). Compared with pure Ni, it has a stronger barrier to atomic diffusion between the silicon (Si) substrate and the upper metal Ag, thereby improving long-term reliability. Second, the addition of V increases the melting point and hardness of the alloy, making the NiV barrier layer more stable in high-temperature processes or working environments, less prone to creep or peeling, improving the mechanical integrity of the multilayer structure, and also significantly improving its thermal stability and mechanical strength. Third, the NiV alloy can form a more uniform and low-resistance interface with the bottom metal (such as titanium Ti). Combined with its good diffusion barrier characteristics, it helps to achieve more stable low-ohmic contact and improve the device conduction efficiency. Meanwhile, by combining the optimized novel dual-stage pulsed magnetron sputtering process, and utilizing its high ionization rate characteristics and the mixed target-avoidance mechanism of cascade collision of coating particles and electron thermal emission, a synergistic improvement in high thermal conductivity of the coating and strong bonding between the film and substrate interface is achieved. (2) The structure of the gradient composite coating of the present invention is a Ti metal adhesion layer, a NiV metal barrier layer and an Ag anti-oxidation high thermal conductivity layer. This gradient composite coating has the advantages of excellent thermal conductivity of NiV metal barrier layer and Ag anti-oxidation high thermal conductivity layer as well as the effect of metal atom interdiffusion suppression, and at the same time has excellent Si-Ti interface bonding strength. (3) The method of the present invention first deposits a Ti metal adhesion layer on the surface of an n-type Si substrate, and then deposits a NiV metal barrier layer and an Ag anti-oxidation high thermal conductivity layer in sequence. The deposition process of the three heterogeneous coatings is divided into two deposition stages: weak ionization and strong ionization. The substrate is heated at high temperature before the Ag anti-oxidation high thermal conductivity layer is deposited, so that the composite coating has a dense coating structure, a smooth and uniform surface quality, and low internal stress and high bonding force between the heterogeneous coatings. This solves the problem that it is currently difficult to obtain a good high thermal conductivity and strong bonding IGBT back gold coating on the surface of an n-type Si substrate by DC magnetron sputtering deposition method. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the electric field design for the two-stage high-power pulsed magnetron sputtering method of the present invention; Figure 2 This is a surface SEM image of the Ti / NiV / Ag gradient composite coating on the n-type Si substrate prepared in Example 1 of this invention; Figure 3 This is a cross-sectional SEM image of the Ti / NiV / Ag gradient composite coating on the surface of the n-type Si substrate prepared in Example 1 of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0022] This invention relates to a high thermal conductivity and strong bonding IGBT back-gold gradient composite coating, which consists of a Ti metal adhesion layer, a NiV metal barrier layer, and an Ag anti-oxidation and high thermal conductivity layer deposited sequentially from the inside to the outside on the surface of an n-type Si substrate. The thickness of the Ti metal adhesion layer is 100nm~300nm, the thickness of the NiV metal barrier layer is 400nm~500nm, and the thickness of the Ag anti-oxidation and high thermal conductivity layer is 600nm~1500nm. The composite coating is composed of uniform and dense nanocrystals with a grain size of less than 50nm.

[0023] The present invention discloses a method for preparing a high thermal conductivity and strong bonding IGBT back-gold gradient composite coating. Before the deposition of the NiV metal barrier layer, a Ti metal adhesion layer is designed. Before the deposition of the Ag anti-oxidation and high thermal conductivity layer, the substrate is heated at high temperature using a substrate heating box device to reduce internal stress and activate the surface, thereby improving the bonding force between the NiV and Ag heterogeneous coatings.

[0024] This invention employs a self-developed dual-stage high-power pulsed magnetron sputtering device with a substrate heating chamber. Specifically, it adds a dual-stage high-power pulsed power supply with gradients incorporating weak and strong ionization electric fields to the power system of an existing DC magnetron sputtering device, while simultaneously loading a substrate heating chamber to heat the substrate. This dual-stage high-power pulsed magnetron sputtering device can provide both ordinary DC and dual-stage high-power pulsed power supply modes. The maximum power of the pulsed power supply is 15kW, the duty cycle τ is adjustable from 5% to 100%, and the pulse conduction width T... on and pulse turn-off width T off It can be configured as needed.

[0025] like Figure 1The diagram shows the electric field design of the dual-stage high-power pulsed magnetron sputtering method of this invention. This invention proposes a design concept of pre-ionization to generate low-energy plasma and strong ionization to further improve the ionization rate, thereby enhancing deposition efficiency. The electric field mode is designed as segmented or stepped, meaning that within one pulse conduction cycle, there are two continuous and independently adjustable pulse stages with a duty cycle τ of 5% to 100%. In the first pulse stage, lower power is applied to initially ionize Ar gas, forming a low-density plasma, defined as the weak ionization stage. In the second pulse stage, higher power is applied to further ionize atoms, forming a high-density plasma, defined as the strong ionization stage. The pre-ionization process in the weak ionization stage reduces internal stress and improves film-substrate adhesion, while the strong ionization process in the strong ionization stage significantly improves deposition efficiency. A substrate heating chamber device is used to improve the adhesion between heterogeneous coatings.

[0026] The method for preparing a high thermal conductivity, strong bonding IGBT back-gold gradient composite coating of the present invention is specifically implemented according to the following steps: First, a Ti metal target with a purity of 99.95%, a NiV alloy target (Ni and V mass percentages of 93wt% and 7wt%, respectively), and an Ag target are installed in a two-stage high-power pulsed magnetron sputtering cavity. The n-type Si substrate is then installed on a substrate rotating frame, with a rotation speed preferably of 5-10 rpm, more preferably 8 rpm.

[0027] Step 1, Ion cleaning: A dual-stage high-power pulsed power supply is turned on. After the vacuum level in the vacuum chamber reaches a certain value, high-purity argon gas is introduced, the titanium target is activated, and a DC current is applied. High-energy argon ions are used to bombard the n-type Si substrate, improving the surface cleanliness and activating the surface. The vacuum level in the vacuum chamber is 2.5~3.0×10⁻⁶. -5 Torr, preferably 3.0×10 -5 Torr; Argon flow rate is 40~50mL / min, preferably 45mL / min; Titanium target current is DC 1.5~2.0A, preferably 1.8A; Cleaning time is 5~8min.

[0028] Step 2, Ti metal adhesion layer deposition: After ion cleaning, the Ti target sputtering mode was activated, and relevant parameters such as peak voltage, pulse on-time width, pulse off-time width, frequency, negative bias voltage, and argon flow rate were set for the weak and strong ionization stages to deposit a pure metallic Ti adhesion layer on the substrate. Specifically, the peak voltages for the weak and strong ionization stages were 200–250 V and 600–700 V, respectively; the pulse on-time widths were 4–8 ms and 8–10 ms, respectively; the pulse off-time width was 10–12 ms; the negative bias voltage was -60–-40 V, preferably -60 V; the frequency was 50–60 Hz, preferably 55 Hz; the argon flow rate was 40–60 mL / min, preferably 55 mL / min; and the deposition time was 5–10 min.

[0029] Step 3, NiV metal barrier layer deposition: After the Ti metal adhesion layer deposition is completed, the Ti target is turned off, and the NiV (93wt%-7wt%) alloy target is turned on. Parameters such as peak voltage, pulse on-time width, negative bias voltage, pulse off-time width, argon flow rate, frequency, and negative bias voltage are set for the weak and strong ionization stages. A NiV metal barrier layer is then deposited on the Ti metal adhesion layer. Specifically, the peak voltages for the weak and strong ionization stages are 200-300V and 650-800V, respectively; the pulse on-time widths are 4-8ms and 8-10ms, respectively; the pulse off-time width is 10-12ms; the argon flow rate is 40-50mL / min, preferably 45mL / min; the frequency is 50-60Hz, preferably 55Hz; the negative bias voltage is -65 to -50V, preferably -60V; and the deposition time is 10-15min.

[0030] Step 4, heating the substrate: After the NiV metal barrier coating is deposited, the NiV (93wt%-7wt%) alloy target is turned off, and the substrate is heated using a substrate heating chamber to reduce residual stress and improve the adhesion between NiV and the Ag heterostructure coating. The heating temperature is 400~450℃, preferably 450℃, and the heating time is 8~10min, preferably 10min.

[0031] Step 5, Deposition of Ag anti-oxidation and high thermal conductivity layer: After heating, the substrate heating chamber was turned off, the Ag target was turned on, and relevant parameters such as peak voltage, pulse on-time width, pulse off-time width, argon flow rate, frequency, and negative bias were set for the weak and strong ionization stages. An Ag anti-oxidation and high thermal conductivity layer was deposited on the NiV metal barrier layer. Specifically, the peak voltages for the weak and strong ionization stages were 200–300 V and 650–800 V, respectively; the pulse on-time widths were 4–8 ms and 8–10 ms, respectively; the pulse off-time width was 10–12 ms; the argon flow rate was 50–60 mL / min, preferably 55 mL / min; the negative bias was -65–-50 V, preferably -60 V; the frequency was 50–60 Hz, preferably 55 Hz; and the deposition time was 20–50 min.

[0032] Finally, a gradient composite coating with high deposition efficiency, low internal stress, high bonding force, excellent thermal conductivity and high surface quality was prepared on an n-type Si substrate.

[0033] Example 1 Step 1, Ion cleaning: When the vacuum level in the vacuum chamber reaches 2.5 × 10⁻⁶ -5 After Torr, high-purity argon gas with a flow rate of 45 mL / min was introduced, the titanium target was started and a DC current of 1.5 A was applied, and the n-type Si matrix was bombarded with ions for 5 min.

[0034] Step 2, Ti metal adhesion layer deposition: Turn on the Ti target sputtering mode, set the peak voltages for the weak ionization and strong ionization stages to 210V and 600V respectively, the pulse on-width to 4ms and 8ms respectively, the pulse off-width to 12ms, the argon flow rate to 45mL / min, the negative bias voltage to -60V, the frequency to 50Hz, and the deposition time to 10min, depositing a pure metallic Ti adhesion layer on the substrate.

[0035] Step 3, NiV metal barrier layer deposition: Turn off the Ti target and turn on the NiV (93wt%-7wt%) alloy target. Set the peak voltages for the weak ionization and strong ionization stages to 220V and 650V, respectively. Set the pulse on-width to 6ms and 8ms, respectively. Set the pulse off-width to 10ms, the negative bias voltage to -55V, the frequency to 55Hz, the argon flow rate to 40mL / min, and the deposition time to 10min. Deposit the NiV metal barrier layer on the Ti metal adhesion layer.

[0036] Step 4, substrate heating: Turn off the NiV (93wt%-7wt%) alloy target and use the substrate heating box device to heat the substrate at a temperature of 400℃ for 8 minutes.

[0037] Step 5, Ag anti-oxidation and high thermal conductivity layer deposition: Turn off the substrate heating box, turn on the Ag target, set the peak voltages for the weak ionization and strong ionization stages to 220V and 650V respectively, the pulse on-width to 4ms and 8ms respectively, the pulse off-width to 10ms, the negative bias voltage to -60V, the frequency to 50Hz, the argon flow rate to 50mL / min, and the deposition time to 20min, depositing an Ag anti-oxidation and high thermal conductivity layer on the NiV metal impedance layer.

[0038] Figure 2 (a), (b), and (c) are SEM images of the Ti, NiV, and Ag coatings prepared in this embodiment, respectively. It can be seen that their surface morphology consists of fine and uniform flower-like, round-like, and gravel-like particles, respectively, without obvious defects and impurities, and the surface quality is good. Figure 3 The cross-sectional SEM image of the Ti / NiV / Ag gradient composite coating prepared in this embodiment shows that the thickness of the Ti metal adhesion layer is 122.5 nm, the thickness of the NiV metal impedance layer is 402.3 nm, and the thickness of the Ag anti-oxidation and high thermal conductivity layer is 610.5 nm. The surface roughness of the gradient composite coating was measured to be 32 nm using laser confocal microscopy; the critical load for film-substrate peeling was measured to be 22.5 N using an automatic scratch tester; the overall thermal conductivity of the gradient composite coating was measured to be 125 W / (m•K) using the steady-state heat flow method; and the nanohardness was measured to be 3.3 GPa using a nanoindenter. After high-temperature treatment at 350℃ for 200 hours, the NiV barrier layer showed good blocking effect against both Ti and Ag metals. Compared with traditional DC magnetron sputtering deposited back-gold coatings, the coating of this invention has better quality and significantly improved performance.

[0039] In summary, the Ti / NiV / Ag gradient composite coating obtained in this embodiment has a dense overall structure, a smooth and defect-free surface, and exhibits excellent performance in terms of film-substrate bonding strength, thermal conductivity, hardness, and metal element blocking effect.

[0040] Example 2 Step 1, Ion cleaning: When the vacuum level in the vacuum chamber reaches 2.8 × 10⁻⁶ -5 After Torr, high-purity argon gas with a flow rate of 45 mL / min was introduced, the titanium target was started and a DC current of 1.6 A was applied, and the n-type Si matrix was bombarded with ions for 8 min.

[0041] Step 2, Ti metal adhesion layer deposition: Turn on the Ti target sputtering mode, set the peak voltages for the weak ionization and strong ionization stages to 220V and 625V respectively, the pulse on-width to 5ms and 9ms respectively, the pulse off-width to 10ms, the argon flow rate to 40mL / min, the negative bias voltage to -40V, the frequency to 55Hz, and the deposition time to 10min, depositing a pure metallic Ti adhesion layer on the substrate.

[0042] Step 3, NiV metal barrier layer deposition: Turn off the Ti target and turn on the NiV (93wt%-7wt%) alloy target. Set the peak voltages for the weak ionization and strong ionization stages to 200V and 680V, ​​respectively. Set the pulse on-width to 5ms and 9ms, the pulse off-width to 10ms, the negative bias to -50V, the frequency to 50Hz, the argon flow rate to 45mL / min, and the deposition time to 10min. Deposit the NiV metal barrier layer on the Ti metal adhesion layer.

[0043] Step 4, substrate heating: Turn off the NiV (93wt%-7wt%) alloy target and use the substrate heating box device to heat the substrate at a temperature of 425℃ for 9 minutes.

[0044] Step 5, Ag anti-oxidation and high thermal conductivity layer deposition: Turn off the substrate heating box, turn on the Ag target, set the peak voltages for the weak ionization and strong ionization stages to 240V and 650V respectively, the pulse on-time widths to 5ms and 9ms respectively, the pulse off-time width to 10ms, the negative bias voltage to -50V, the frequency to 55Hz, the argon flow rate to 55mL / min, and the deposition time to 25min, depositing an Ag anti-oxidation and high thermal conductivity layer on the NiV metal impedance layer.

[0045] The performance of the composite coating obtained in this embodiment was tested. SEM images of its surface showed that the surface morphology still consisted of fine, uniform flower-like, cellular, and gravel-like particles, with no obvious defects or impurities, indicating good surface quality. Cross-sectional SEM images of the coating showed that the Ti metal adhesion layer thickness was 134.8 nm, the NiV metal impedance layer thickness was 410.6 nm, and the Ag anti-oxidation high thermal conductivity layer thickness was 725.2 nm. The surface roughness of the gradient composite coating was measured to be 28.6 nm using laser confocal microscopy. The critical load for film-substrate peeling of the gradient composite coating was measured to be 21.2 N using an automatic scratch tester. The overall thermal conductivity of the gradient composite coating was measured to be 115.4 W / (m•K) using the steady-state heat flow method. The nanohardness of the gradient composite coating was measured to be 3.02 GPa using a nanoindenter. After high-temperature treatment at 300℃ for 200 hours, the NiV barrier layer showed good blocking effect against both Ti and Ag metals.

[0046] Example 3 Step 1, Ion cleaning: When the vacuum level in the vacuum chamber reaches 3.0 × 10⁻⁶ -5 After Torr, high-purity argon gas with a flow rate of 40 mL / min was introduced, the titanium target was started and a DC current of 1.7 A was applied, and the n-type Si matrix was bombarded with ions for 8 min.

[0047] Step 2, Ti metal adhesion layer deposition: Turn on the Ti target sputtering mode, set the peak voltages for the weak ionization and strong ionization stages to 230V and 650V respectively, the pulse on-width to 6ms and 8ms respectively, the pulse off-width to 10ms, the argon flow rate to 50mL / min, the negative bias voltage to -55V, the frequency to 55Hz, and the deposition time to 8min, depositing a pure metallic Ti adhesion layer on the substrate.

[0048] Step 3, NiV metal barrier layer deposition: Turn off the Ti target and turn on the NiV (93wt%-7wt%) alloy target. Set the peak voltages for the weak ionization and strong ionization stages to 240V and 700V, respectively. Set the pulse on-width to 6ms and 8ms, the pulse off-width to 8ms, the negative bias voltage to -55V, the frequency to 60Hz, the argon flow rate to 45mL / min, and the deposition time to 12min. Deposit the NiV metal barrier layer on the Ti metal adhesion layer.

[0049] Step 4, substrate heating: Turn off the NiV (93wt%-7wt%) alloy target and use the substrate heating box device to heat the substrate at a temperature of 400℃ for 10 minutes.

[0050] Step 5, Ag oxidation-resistant and high thermal conductivity layer deposition: Turn off the substrate heating box, turn on the Ag target, set the peak voltages for the weak ionization and strong ionization stages to 250V and 700V respectively, the pulse on-time widths to 6ms and 10ms respectively, the pulse off-time width to 10ms, the negative bias voltage to -55V, the frequency to 60Hz, the argon flow rate to 55mL / min, and the deposition time to 30min, depositing an Ag oxidation-resistant and high thermal conductivity layer on the NiV metal impedance layer.

[0051] The composite coating obtained in this embodiment was subjected to performance testing. SEM images of its surface showed that the surface morphology still consisted of fine, uniform flower-like, cellular, and gravel-like particles, with no obvious defects or impurities, indicating good surface quality. Cross-sectional SEM images of the coating showed that the Ti metal adhesion layer thickness was 145.6 nm, the NiV metal impedance layer thickness was 422.8 nm, and the Ag anti-oxidation high thermal conductivity layer thickness was 835.7 nm. The surface roughness of the gradient composite coating was measured to be 28.2 nm using laser confocal microscopy; the critical load for film-substrate peeling was measured to be 23.4 N using an automatic scratch tester; the overall thermal conductivity of the gradient composite coating was measured to be 126.4 W / (m•K) using the steady-state heat flow method; and the nanohardness was measured to be 3.35 GPa using a nanoindenter. After high-temperature treatment at 300℃ for 200 hours, the NiV barrier layer showed good blocking effect against both Ti and Ag metals.

[0052] Example 4 Step 1, Ion cleaning: When the vacuum level in the vacuum chamber reaches 2.8 × 10⁻⁶ -5 After Torr, high-purity argon gas with a flow rate of 45 mL / min was introduced, the titanium target was started and a DC current of 1.8 A was applied, and the n-type Si matrix was bombarded with ions for 7 min.

[0053] Step 2, Ti metal adhesion layer deposition: Turn on the Ti target sputtering mode, set the peak voltages for the weak ionization and strong ionization stages to 240V and 675V respectively, the pulse on-width to 7ms and 9ms respectively, the pulse off-width to 11ms, the argon flow rate to 45mL / min, the negative bias voltage to -50V, the frequency to 55Hz, and the deposition time to 7min, depositing a pure metallic Ti adhesion layer on the substrate.

[0054] Step 3, NiV metal barrier layer deposition: Turn off the Ti target and turn on the NiV (93wt%-7wt%) alloy target. Set the peak voltages for the weak ionization and strong ionization stages to 250V and 720V, respectively. Set the pulse on-width to 4ms and 10ms, respectively. Set the pulse off-width to 10ms, the negative bias voltage to -60V, the frequency to 55Hz, the argon flow rate to 50mL / min, and the deposition time to 13min. Deposit the NiV metal barrier layer on the Ti metal adhesion layer.

[0055] Step 4, substrate heating: Turn off the NiV (93wt%-7wt%) alloy target and use the substrate heating box device to heat the substrate at a temperature of 425℃ for 8 minutes.

[0056] Step 5, Ag oxidation-resistant and high thermal conductivity layer deposition: Turn off the substrate heating box, turn on the Ag target, set the peak voltages for the weak ionization and strong ionization stages to 260V and 730V respectively, the pulse on-time widths to 7ms and 10ms respectively, the pulse off-time width to 10ms, the negative bias voltage to -55V, the frequency to 50Hz, the argon flow rate to 60mL / min, and the deposition time to 35min, depositing an Ag oxidation-resistant and high thermal conductivity layer on the NiV metal impedance layer.

[0057] The performance of the composite coating obtained in this embodiment was tested. SEM images of its surface showed that the surface morphology still consisted of fine, uniform flower-like, cellular, and gravel-like particles, with no obvious defects or impurities, indicating good surface quality. Cross-sectional SEM images of the coating showed that the Ti metal adhesion layer thickness was 145.6 nm, the NiV metal impedance layer thickness was 450.6 nm, and the Ag anti-oxidation high thermal conductivity layer thickness was 986.4 nm. The surface roughness of the gradient composite coating was measured to be 26.8 nm using laser confocal microscopy; the critical load for film-substrate peeling was measured to be 24.6 N using an automatic scratch tester; the overall thermal conductivity of the gradient composite coating was measured to be 130.5 W / (m•K) using the steady-state heat flow method; and the nanohardness was measured to be 3.46 GPa using a nanoindenter. After high-temperature treatment at 300℃ for 200 hours, the NiV barrier layer showed good blocking effect against both Ti and Ag metals.

[0058] Example 5 Step 1, Ion cleaning: When the vacuum level in the vacuum chamber reaches 3.0 × 10⁻⁶ -5 After Torr, high-purity argon gas with a flow rate of 45 mL / min was introduced, the titanium target was started and a DC current of 1.5 A was applied, and the n-type Si matrix was bombarded with ions for 6 min.

[0059] Step 2, Ti metal adhesion layer deposition: Turn on the Ti target sputtering mode, set the peak voltages for the weak ionization and strong ionization stages to 250V and 700V respectively, the pulse on-width to 6ms and 10ms respectively, the pulse off-width to 12ms, the argon flow rate to 50mL / min, the negative bias voltage to -60V, the frequency to 55Hz, and the deposition time to 8min, depositing a pure metallic Ti adhesion layer on the substrate.

[0060] Step 3, NiV metal barrier layer deposition: Turn off the Ti target and turn on the NiV (93wt%-7wt%) alloy target. Set the peak voltages for the weak ionization and strong ionization stages to 270V and 750V, respectively. Set the pulse on-width to 5ms and 8ms, the pulse off-width to 10ms, the negative bias to -60V, the frequency to 60Hz, the argon flow rate to 45mL / min, and the deposition time to 14min. Deposit the NiV metal barrier layer on the Ti metal adhesion layer.

[0061] Step 4, substrate heating: Turn off the NiV (93wt%-7wt%) alloy target and use the substrate heating box device to heat the substrate at a temperature of 450℃ for 9 minutes.

[0062] Step 5, Ag oxidation-resistant and high thermal conductivity layer deposition: Turn off the substrate heating box, turn on the Ag target, set the peak voltages for the weak ionization and strong ionization stages to 280V and 760V respectively, the pulse on-width to 8ms and 8ms respectively, the pulse off-width to 10ms, the negative bias voltage to -55V, the frequency to 55Hz, the argon flow rate to 55mL / min, and the deposition time to 40min, depositing an Ag oxidation-resistant and high thermal conductivity layer on the NiV metal impedance layer.

[0063] The composite coating obtained in this embodiment was subjected to performance testing. SEM images of its surface showed that the surface morphology still consisted of fine, uniform flower-like, cellular, and gravel-like particles, with no obvious defects or impurities, indicating good surface quality. Cross-sectional SEM images of the coating showed that the Ti metal adhesion layer thickness was 230.4 nm, the NiV metal impedance layer thickness was 472.5 nm, and the Ag anti-oxidation high thermal conductivity layer thickness was 1267.4 nm. The surface roughness of the gradient composite coating was measured to be 26.3 nm using laser confocal microscopy; the critical load for film-substrate peeling was measured to be 26.8 N using an automatic scratch tester; the overall thermal conductivity of the gradient composite coating was measured to be 136.2 W / (m•K) using the steady-state heat flow method; and the nanohardness was measured to be 3.52 GPa using a nanoindenter. After high-temperature treatment at 300℃ for 200 hours, the NiV barrier layer showed good blocking effect against both Ti and Ag metals.

[0064] Example 6 Step 1, Ion cleaning: When the vacuum level in the vacuum chamber reaches 3.0 × 10⁻⁶ -5 After Torr, high-purity argon gas with a flow rate of 50 mL / min was introduced, the titanium target was started and a DC current of 1.5 A was applied, and the n-type Si matrix was bombarded with ions for 5 min.

[0065] Step 2, Ti metal adhesion layer deposition: Turn on the Ti target sputtering mode, set the peak voltages for the weak ionization and strong ionization stages to 250V and 700V respectively, the pulse on-width to 6ms and 10ms respectively, the pulse off-width to 10ms, the argon flow rate to 60mL / min, the negative bias voltage to -55V, the frequency to 60Hz, and the deposition time to 10min, depositing a pure metallic Ti adhesion layer on the substrate.

[0066] Step 3, NiV metal barrier layer deposition: Turn off the Ti target and turn on the NiV (93wt%-7wt%) alloy target. Set the peak voltages for the weak ionization and strong ionization stages to 300V and 800V, respectively. Set the pulse on-time widths to 6ms and 8ms, respectively. Set the pulse off-time width to 10ms, the negative bias voltage to -60V, the frequency to 55Hz, the argon flow rate to 50mL / min, and the deposition time to 15min. Deposit the NiV metal barrier layer on the Ti metal adhesion layer.

[0067] Step 4, substrate heating: Turn off the NiV (93wt%-7wt%) alloy target and use the substrate heating box device to heat the substrate at a temperature of 450℃ for 8 minutes.

[0068] Step 5, Ag oxidation-resistant and high thermal conductivity layer deposition: Turn off the substrate heating box, turn on the Ag target, set the peak voltages for the weak ionization and strong ionization stages to 300V and 800V respectively, the pulse on-time widths to 6ms and 8ms respectively, the pulse off-time width to 10ms, the negative bias voltage to -60V, the frequency to 60Hz, the argon flow rate to 60mL / min, and the deposition time to 50min, depositing an Ag oxidation-resistant and high thermal conductivity layer on the NiV metal impedance layer.

[0069] The composite coating obtained in this embodiment was subjected to performance testing. SEM images of its surface showed that the surface morphology still consisted of fine, uniform flower-like, round-like, and gravel-like particles, with no obvious defects or impurities, indicating good surface quality. Cross-sectional SEM images of the coating showed that the Ti metal adhesion layer thickness was 284.6 nm, the NiV metal impedance layer thickness was 496.2 nm, and the Ag anti-oxidation high thermal conductivity layer thickness was 1486.5 nm. The surface roughness of the gradient composite coating was measured to be 27.4 nm using laser confocal microscopy; the critical load for film-substrate peeling was measured to be 25.6 N using an automatic scratch tester; the overall thermal conductivity of the gradient composite coating was measured to be 135.0 W / (m•K) using the steady-state heat flow method; and the nanohardness was measured to be 3.43 GPa using a nanoindenter. After high-temperature treatment at 300℃ for 200 hours, the NiV barrier layer showed good blocking effect against both Ti and Ag metals.

Claims

1. A high thermal conductivity, strong bonding gradient composite coating for IGBT back-gold, characterized in that, It includes a Ti metal adhesion layer, a NiV metal barrier layer, and an Ag anti-oxidation and high thermal conductivity layer deposited sequentially from the inside to the outside on the n-type Si substrate surface.

2. The high thermal conductivity and strong bonding IGBT back-gold gradient composite coating according to claim 1, characterized in that, The thickness of the Ti metal adhesion layer is 100nm~300nm, the thickness of the NiV metal barrier layer is 400nm~500nm, and the thickness of the Ag anti-oxidation high thermal conductivity layer is 600nm~1500nm; the gradient composite coating is composed of uniform and dense nanocrystals with a grain size of less than 50nm.

3. A method for preparing a high thermal conductivity, strong bonding IGBT back-gold gradient composite coating, characterized in that, Specifically: Step 1: Under vacuum conditions, argon gas is introduced, and the n-type Si substrate is cleaned by ion bombardment using a Ti target. Step 2: Turn on the Ti target sputtering mode and deposit a Ti metal adhesion layer on the substrate surface by controlling the two discharge stages of weak ionization and strong ionization. Step 3: Turn off the Ti target and turn on the NiV alloy target. By controlling the two discharge stages of weak and strong ionization, deposit a NiV metal barrier layer on the Ti metal adhesion layer. Step 4: Turn off the NiV target and heat the substrate; Step 5: Turn on the Ag target and deposit an Ag anti-oxidation and high thermal conductivity layer on the NiV metal barrier layer by controlling the two discharge stages of weak and strong ionization.

4. The method for preparing a high thermal conductivity, strong bonding IGBT back-gold gradient composite coating according to claim 3, characterized in that, In step 1, the vacuum degree is 2.5 × 10⁻⁶. -5 ~3.0×10 -5 Torr, argon flow rate 40~50mL / min, metal Ti target current DC 1.5~2.0A, cleaning time 5~8min.

5. The method for preparing a high thermal conductivity, strong bonding IGBT back-gold gradient composite coating according to claim 3, characterized in that, In step 2, the peak voltages for the weak ionization and strong ionization stages are 200~250V and 600~700V, respectively; the pulse on-widths are 4~8ms and 8~10ms, respectively; the pulse off-width is 10~12ms; the argon flow rate is 40~60mL / min; the negative bias voltage is -60~-40V; the frequency is 50~60Hz; and the deposition time is 5~10min.

6. The method for preparing a high thermal conductivity, strong bonding IGBT back-gold gradient composite coating according to claim 3, characterized in that, In step 3, the peak voltages for the weak ionization and strong ionization stages are 200~300V and 650~800V, respectively; the pulse on-widths are 4~8ms and 8~10ms, respectively; the pulse off-width is 10~12ms; the argon flow rate is 40~50mL / min; the frequency is 50~60Hz; the negative bias is -65~-50V; and the deposition time is 10~15min.

7. The method for preparing a high thermal conductivity, strong bonding IGBT back-gold gradient composite coating according to claim 3, characterized in that, In step 4, the heating temperature is 400~450℃ and the heating time is 8~10min.

8. The method for preparing a high thermal conductivity, strong bonding IGBT back-gold gradient composite coating according to claim 3, characterized in that, In step 5, the peak voltages for the weak ionization and strong ionization stages are 200~300V and 650~800V, respectively; the pulse on-widths are 4~8ms and 8~10ms, respectively; the pulse off-width is 10~12ms; the argon flow rate is 50~60mL / min; the negative bias voltage is -65~-50V; the frequency is 50~60Hz; and the deposition time is 20~50min.

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