阅读说明：本技术 一种金刚石散热片的表面平滑化及连接方法 (Surface smoothing and connecting method of diamond radiating fin ) 是由 赵柯臣 赵继文 代兵 曹文鑫 朱嘉琦 韩杰才 于 2021-09-24 设计创作，主要内容包括：一种金刚石散热片的表面平滑化及连接方法,涉及金刚石散热片的连接方法。本发明要解决利用纳米/微米金属烧结技术键合时,大尺寸连接存在压力过大对器件的可靠性影响大,若无压烧结则只能实现小尺寸连接,且烧结层孔隙率大,严重影响其导热性和可靠性的问题,解决利用原子扩散键合技术键合时,存在对金刚石材料表面粗糙度要求高,需要超真空,金刚石和硅片镀完金属层后未及时压合会导致键合效果不佳的问题。方法：一、沉积过渡层金属/金复合金属镀层；二、涂覆纳米金属浆料并热压烧结键合；三、模板剥离并保留金刚石上金属层；四、表面活化清洗；五、键合。本发明用于金刚石散热片的表面平滑化及连接。(A surface smoothing and connecting method of a diamond radiating fin relates to a connecting method of the diamond radiating fin. The invention aims to solve the problems that when a nano/micron metal sintering technology is used for bonding, the influence on the reliability of a device is large due to overlarge pressure of large-size connection, only small-size connection can be realized if pressureless sintering is carried out, the porosity of a sintering layer is large, and the thermal conductivity and the reliability of the device are seriously influenced, and solve the problems that when the atomic diffusion bonding technology is used for bonding, the requirement on the surface roughness of a diamond material is high, ultra-vacuum is needed, and the bonding effect is poor due to untimely bonding of the diamond and a silicon wafer after a metal layer is plated. The method comprises the following steps: firstly, depositing a transition layer metal/gold composite metal coating; coating nano metal slurry and hot-pressing, sintering and bonding; thirdly, stripping the template and reserving the metal layer on the diamond; fourthly, surface activation cleaning; and fifthly, bonding. The invention is used for smoothing and connecting the surface of the diamond cooling fin.)

1. A surface smoothing and connecting method of a diamond cooling fin is characterized by comprising the following steps:

firstly, depositing a transition layer metal/gold composite metal coating:

sequentially cleaning the template, the diamond sheet and the semiconductor chip material and cleaning the diamond sheet and the semiconductor chip material by argon plasma, and then sequentially plating a transition layer metal layer of 10 nm-20 nm and a gold layer of 100 nm-200 nm on the template, the diamond sheet and the semiconductor chip material by adopting a high-vacuum degree magnetron sputtering system to obtain the template with a deposited transition layer metal/gold composite metal coating, the diamond sheet with a deposited transition layer metal/gold composite metal coating and the semiconductor chip material with a deposited transition layer metal/gold composite metal coating;

coating nano metal slurry and hot-pressing sintering bonding:

respectively coating the nano metal slurry on a template on which a transition layer metal/gold composite metal coating is deposited and the surface of one side of a diamond sheet on which the transition layer metal/gold composite metal coating is deposited, preserving heat for 30-60 min at the temperature of 120-160 ℃, then aligning and bonding, and preserving heat for 0.5-1 h at the temperature of 180-280 ℃ and under the condition that the surface applied pressure is not less than 20MPa to obtain a material after hot-pressing sintering bonding;

thirdly, stripping the template and keeping the metal layer on the diamond:

dipping the material subjected to hot-pressing sintering bonding in a stripping solution, dissolving and stripping the template to obtain a diamond sheet with a nano metal layer and a transition layer metal/gold composite metal coating;

fourthly, surface activation cleaning:

cleaning and drying the diamond sheet with the nano metal layer and the transition layer metal/gold composite metal coating, and then carrying out argon plasma cleaning on the diamond sheet with the nano metal layer and the transition layer metal/gold composite metal coating and the semiconductor chip material with the transition layer metal/gold composite metal coating deposited to obtain a diamond sheet with a surface activated and cleaned and a semiconductor chip material with a surface activated and cleaned;

and V, bonding:

and (3) attaching the diamond sheet with the surface activated and cleaned and the semiconductor chip material with the surface activated and cleaned, and then transferring the diamond sheet and the semiconductor chip material into hot-pressing equipment for bonding connection to finish the surface smoothing and connection method of the diamond cooling fin.

2. The method of claim 1, wherein the template in step one is a quartz plate with a roughness less than 1 nm; the semiconductor chip material in the first step is silicon, silicon carbide, gallium nitride or gallium oxide; the transition layer metal in the first step is one or more of Ti, Mo, Cr, Ni and W; the surface roughness of the diamond sheet in the first step is less than 1 micron.

3. The method of claim 1, wherein the cleaning in the first step comprises ultrasonic cleaning with acetone and alcohol for 5-10 min, washing with deionized water, and oven drying.

4. The method as claimed in claim 1, wherein the argon plasma cleaning in the step one is performed for 20s to 120s under a pressure of 10Pa to 100Pa, a power of 100W to 200W, and an argon flow of 20sccm to 60 sccm.

5. The method as claimed in claim 1, wherein the step one comprises a step of applying a high vacuum magnetron sputtering system to the template, the diamond wafer and the semiconductor chip respectivelyThe material is sequentially plated with a transition layer metal layer of 10 nm-20 nm and a gold layer of 100 nm-200 nm, and the method specifically comprises the following steps: keeping the target base distance at 80-100 mm, firstly vacuumizing to 5 × 10^-4Pa～10×10^-4Pa, starting under the conditions that the argon flow is 20 sccm-40 sccm, the radio frequency power supply power is 40W-60W and the pressure is 3 Pa-5 Pa, and then sequentially sputtering the transition layer metal layer and the gold layer under the conditions that the argon flow is 20 sccm-40 sccm, the radio frequency power supply power is 40W-60W and the pressure is 0.5 Pa-1 Pa.

6. The method according to claim 1, wherein the mass percentage of the nano metal particles in the nano metal slurry in the second step is 80-90%; the nano metal particles are one or a mixture of several of nano silver, nano copper and nano gold.

7. The method for smoothing and connecting the surface of a diamond heat sink according to claim 1, wherein in the second step, ultra-thin stencil printing is used to coat the nano-metal slurry on the surface of the stencil on which the transition layer metal/gold composite metal plating layer is deposited and the surface of the diamond plate on which the transition layer metal/gold composite metal plating layer is deposited, respectively, and the coating thickness is 5 μm to 100 μm.

8. The method according to claim 1, wherein the stripping solution in step three is a hydrofluoric acid solution with a mass percentage of 1% to 10%.

9. The method of claim 1, wherein the argon plasma cleaning in the fourth step is performed for 20-120 s under the conditions of a pressure of 10-100 Pa, a power of 100-200W and an argon flow of 20-60 sccm.

10. The method of claim 1, wherein the bonding connection is performed at a pressure of 5MPa or less and at a temperature of room temperature to 200 ℃ for 10min to 30min in step five.

Technical Field

The invention relates to a method for connecting diamond cooling fins.

Background

High density, high power and high performance have been the inevitable trends in chip development, but the problems of chip damage and device failure due to heat generation have been followed. The traditional heat dissipation material has the problems of poor heat conductivity, incompatible size and framework and the like, and can also cause uneven hot spot distribution, the temperature difference on the chip reaches 10-20 ℃, and the high-efficiency heat dissipation of the ultrahigh heat flow density device is difficult to realize. Because the diamond has excellent performances of high heat conduction, high temperature resistance, corrosion resistance and the like, the chip can be quickly equalized in temperature to eliminate local hot spots, the heat dissipation pressure of the whole structure is effectively reduced, the bearable specification/performance of the chip can be improved under the same heat dissipation capacity, or the specification/performance can be maintained unchanged to reduce the heat dissipation cost; the upper limit of the power consumption of the sealed chip is enhanced, the overall performance and the reliability of the chip are improved, and efficient heat dissipation in the high-frequency and high-power microelectronic field is expected to be realized.

The diamond heat dissipation technology not only has great application value in the aspect of heat dissipation of devices with ultrahigh heat flux density, but also has important technical support function in key fields of heat dissipation of optical modules, integrated circuits, high-density interconnection and the like. However, the material technology still faces the following problems in the chip packaging system:

1. the diamond material has stable chemical property and high hardness, and is polished efficiently and excellently by adopting a Chemical Mechanical Polishing (CMP) method to obtain a smooth surface with sub-nanometer roughness, so that the diamond material has the problems of high difficulty, unstable yield, time-consuming polishing, higher cost, incompatibility with front and rear process flows and the like, and the application of the diamond material is limited to a certain extent. Furthermore, the CMP process is not suitable for three-dimensional structured substrate surfaces, such as the bottom surfaces of etch cavities for micro-electromechanical system (MEMS) based sensing devices.

2. The diamond material needs to form high-precision bonding with a heterogeneous material so as to realize efficient heat dissipation. The conventional bonding process, such as Surface Activation Bonding (SAB), Atomic Diffusion Bonding (ADB), fusion bonding (fusion bonding) and the like, is adopted, the requirement on the surface roughness of the bonded material is extremely high, generally reaches 1 nm-2 nm, and the bonding requires the processes of ultrahigh vacuum, pressure application, temperature rise and the like, so that the process is high in complexity, poor in consistency and high in cost. In addition, the transition layer added for reducing the interface thermal resistance is generally small in thickness and large in stress, so that risks such as delamination and fracture are easily caused, and the reliability of the device is influenced.

3. Conventional solder bonding is widely used for device integration because it supports relatively low temperature processes and can withstand surface roughness. However, as a thermal interface material, the thermal conductivity of conventional solders is two orders of magnitude lower than that of diamond, and the thickness of the solder layer is typically greater than 100 μm, which introduces high interface thermal resistance, and thus this approach is generally considered unsuitable for integrating power devices onto diamond.

The metal nano particles have large specific surface area, high activity and high thermal conductivity, so that the rapid sintering bonding at low temperature can be realized. Meanwhile, the requirement on the surface roughness of the bonding material is not high, the complexity of the bonding process is low, and the yield is high. The problems of high cost and the like caused by complex process equipment can be avoided. Therefore, the realization of high-quality bonding of diamond materials and devices by using nano materials is considered to be an important direction for solving the current high heat flux density heat dissipation, but due to the particularity of the diamond materials, the nano material bonding process still has technical difficulties. The technology utilizes the low sintering temperature and the high thermal conductivity of nano/micron-sized metal particles, and the surfaces of two materials are sintered together through metal slurry at a certain temperature and pressure, so that the bonding of the two materials is realized. Generally, it is necessary to increase the pressure during sintering to increase the strength of the bond between the two interfaces to achieve lower porosity. However, the following problems mainly exist in the process of connecting the chip and the substrate: (1) generally, for the connection of large-size surfaces, 10-30 MPa of pressure is required to be applied to reduce the interfacial porosity (no pressure or low pressure)Interface porosity under pressure is about 25%) and improves connection strength, and the reliability of the device is greatly influenced by the excessive pressure. (2) Whereas pressureless sintering is generally only suitable for small-size connections (< 5X 5 mm)²) And the porosity of the sintered layer is high, which seriously influences the thermal conductivity and reliability of the sintered layer.

The atomic diffusion bonding technology of diamond and semiconductor chip material: the technology is characterized in that a nanoscale ultrathin metal layer is plated on the surface of a material to be bonded, the two materials to be bonded are directly contacted at low temperature or even room temperature, and the high-strength bonding of the two materials is realized by utilizing the principle of metal atom diffusion. The technology can solve the strict process problems of high requirement on the surface roughness of the material, requirement on ultra-vacuum and the like in the bonding process to a certain extent, but the surface roughness still needs to be less than 10 nanometers, and for diamond, the polishing difficulty and the cost are higher. Although the atomic diffusion bonding process of diamond and silicon can realize bonding at normal temperature, the following problems still exist: (1) the prior art requires that the surface roughness of the bonded material is within 10 nanometers, but for diamond materials, the polishing of the order of magnitude is realized, the technical difficulty is still high, and the yield is not high. And (2) after the diamond and semiconductor chip materials are plated with the metal layers, in order to prevent the oxidation or adsorption of the metal surfaces, the diamond and semiconductor chip materials need to be quickly transferred into bonding equipment or directly pressed in a vacuum chamber. The whole process has no accurate operation flow, the uncertainty and the risk are large, and the yield of the bonded product cannot be sufficiently ensured.

Disclosure of Invention

The invention aims to solve the problems that when a nano/micron metal sintering technology is used for bonding, the influence on the reliability of a device is large due to overlarge pressure of large-size connection, only small-size connection can be realized if pressureless sintering is carried out, the porosity of a sintering layer is large, and the thermal conductivity and the reliability of the device are seriously influenced, and solve the problems that when the atomic diffusion bonding technology is used for bonding, the requirement on the surface roughness of a diamond material is high, ultra-vacuum is needed, and the bonding effect is poor due to untimely pressing of the diamond and a semiconductor chip material after a metal layer is plated. Further provides a method for smoothing the surface of the diamond heat sink and connecting the diamond heat sink.

A surface smoothing and connecting method of a diamond cooling fin is carried out according to the following steps:

firstly, depositing a transition layer metal/gold composite metal coating:

sequentially cleaning the template, the diamond sheet and the semiconductor chip material and cleaning the diamond sheet and the semiconductor chip material by argon plasma, and then sequentially plating a transition layer metal layer of 10 nm-20 nm and a gold layer of 100 nm-200 nm on the template, the diamond sheet and the semiconductor chip material by adopting a high-vacuum degree magnetron sputtering system to obtain the template with a deposited transition layer metal/gold composite metal coating, the diamond sheet with a deposited transition layer metal/gold composite metal coating and the semiconductor chip material with a deposited transition layer metal/gold composite metal coating;

coating nano metal slurry and hot-pressing sintering bonding:

respectively coating the nano metal slurry on a template on which a transition layer metal/gold composite metal coating is deposited and the surface of one side of a diamond sheet on which the transition layer metal/gold composite metal coating is deposited, preserving heat for 30-60 min at the temperature of 120-160 ℃, then aligning and bonding, and preserving heat for 0.5-1 h at the temperature of 180-280 ℃ and under the condition that the surface applied pressure is not less than 20MPa to obtain a material after hot-pressing sintering bonding;

thirdly, stripping the template and keeping the metal layer on the diamond:

dipping the material subjected to hot-pressing sintering bonding in a stripping solution, dissolving and stripping the template to obtain a diamond sheet with a nano metal layer and a transition layer metal/gold composite metal coating;

fourthly, surface activation cleaning:

cleaning and drying the diamond sheet with the nano metal layer and the transition layer metal/gold composite metal coating, and then carrying out argon plasma cleaning on the diamond sheet with the nano metal layer and the transition layer metal/gold composite metal coating and the semiconductor chip material with the transition layer metal/gold composite metal coating deposited to obtain a diamond sheet with a surface activated and cleaned and a semiconductor chip material with a surface activated and cleaned;

and V, bonding:

and (3) attaching the diamond sheet with the surface activated and cleaned and the semiconductor chip material with the surface activated and cleaned, and then transferring the diamond sheet and the semiconductor chip material into hot-pressing equipment for bonding connection to finish the surface smoothing and connection method of the diamond cooling fin.

The invention has the beneficial effects that:

the invention provides a one-step smoothing method based on film transfer, which adopts nano metal to realize high-quality bonding between diamond with large surface roughness and a semiconductor chip material, and realizes the sintering principle of nano metal particles in low-temperature and normal-pressure atmospheric environment, thereby realizing high-reliability bonding connection between the diamond and the semiconductor chip material.

The technical scheme of the invention carries out rapid smoothing treatment on the diamond; and the subsequent surface activated metal diffusion bonding is combined, a high vacuum environment is not needed, the bonding of the diamond with large surface roughness (hundred nanometers) and the semiconductor chip material is realized, and the complexity and the cost of the prior art are reduced.

1. The one-step film transfer process based on the stripping of the nano metal template utilizes the densification transformation of nano metal particles in the process of pressure sintering to realize the smoothing treatment which is different from the prior art and needs to carry out high-precision polishing on diamond;

2. the subsequent metal diffusion bonding with surface activation is combined, because the gold has good stability and is not easy to be oxidized, high vacuum environment bonding is not needed, the problem of bonding rate reduction caused by long-time exposure of the surface to be bonded is solved, the bonding of diamond with large surface roughness (hundred nanometers) and a semiconductor chip material is realized, the final bonding temperature is not higher than 200 ℃, and the integration of the diamond and a flip chip is completed under the pressure of not more than 5 MPa. Compared with the conventional micro-nano metal sintering connection process, the bonding interface obtained by the method is thinner (5-30 microns) and more compact (the interface porosity is less than 10%), large-size connection is realized, and efficient heat dissipation of a semiconductor chip unit is facilitated.

The invention solves the key bonding problem in the process of enhancing the heat dissipation of the semiconductor chip by utilizing the high-heat-conductivity diamond, and has wide applicability for improving the high-efficiency heat dissipation of a high-heat-flow-density device. The high-heat-density heat dissipation structure can be used for heat dissipation of applications with high heat-flow-density characteristics, such as SiC high-frequency devices, GaN power devices, optical communication modules, TR components for high-frequency communication and the like.

The invention is used for the surface smoothing and connecting method of the diamond cooling fin.

Drawings

FIG. 1 is a schematic flow chart of a method for smoothing and connecting the surface of a diamond heat sink according to the present invention;

FIG. 2 is a scanning microscope photograph of atomic force before and after smoothing of the diamond surface, (a) is a scanning photograph of a 50 μm × 50 μm area of an original diamond piece, (b) is a scanning photograph of a 50 μm × 50 μm area of a diamond piece with a nano metal layer and a chromium/gold composite metal plating layer left in the third step of the example, (c) is a scanning photograph of a 5 μm × 5 μm area of an original diamond piece, and (d) is a scanning photograph of a 5 μm × 5 μm area of a diamond piece with a nano metal layer and a chromium/gold composite metal plating layer left in the third step of the example;

FIG. 3 is a graph showing roughness contrast, (a) is a 50 μm by 50 μm area scan of an original diamond wafer, (b) is a 50 μm by 50 μm area scan of a diamond wafer with a nano-metal layer and a Cr/Au composite metal coating left in the third step of the example, (c) is a 5 μm by 5 μm area scan of an original diamond wafer, and (d) is a 5 μm by 5 μm area scan of a diamond wafer with a nano-metal layer and a Cr/Au composite metal coating left in the third step of the example;

FIG. 4 is a scanning electron microscope image of the diamond-silicon die bonding material interface prepared in example two;

FIG. 5 is a calculated plot of porosity for the interface section of FIG. 4;

FIG. 6 is an atomic force scanning microscope photograph of a diamond before and after smoothing of a diamond surface, (a) is a 50 μm × 50 μm area scanning photograph of an original diamond piece, (b) is a 50 μm × 50 μm area scanning photograph of a diamond piece left with a nano metal layer and a titanium/gold composite metal plating layer in one step of the example, (c) is a 5 μm × 5 μm area scanning photograph of an original diamond piece, and (d) is a 5 μm × 5 μm area scanning photograph of a diamond piece left with a nano metal layer and a titanium/gold composite metal plating layer in one step of the example;

FIG. 7 is a graph showing roughness contrast, (a) is a 50 μm × 50 μm area scan of an original diamond wafer, (b) is a 50 μm × 50 μm area scan of a diamond wafer with a nano-metal layer and a titanium/gold composite metal coating left in the third step of the example, (c) is a 5 μm × 5 μm area scan of an original diamond wafer, and (d) is a 5 μm × 5 μm area scan of a diamond wafer with a nano-metal layer and a titanium/gold composite metal coating left in the third step of the example;

FIG. 8 is a scanning electron microscope image of the diamond-silicon die bonding material interface prepared according to the first example;

FIG. 9 is a calculated plot of porosity for the interface section of FIG. 8;

FIG. 10 is a schematic diagram of a thrust force test principle of the bonding strength of diamond and silicon bare chip;

fig. 11 is a graph comparing the thrust test strength of diamond to silicon die bonded samples.

Detailed Description

The first embodiment is as follows: specifically, referring to fig. 1, the method for smoothing and connecting the surface of a diamond heat sink according to the present embodiment is performed by the following steps:

firstly, depositing a transition layer metal/gold composite metal coating:

sequentially cleaning the template, the diamond sheet and the semiconductor chip material and cleaning the diamond sheet and the semiconductor chip material by argon plasma, and then sequentially plating a transition layer metal layer of 10 nm-20 nm and a gold layer of 100 nm-200 nm on the template, the diamond sheet and the semiconductor chip material by adopting a high-vacuum degree magnetron sputtering system to obtain the template with a deposited transition layer metal/gold composite metal coating, the diamond sheet with a deposited transition layer metal/gold composite metal coating and the semiconductor chip material with a deposited transition layer metal/gold composite metal coating;

coating nano metal slurry and hot-pressing sintering bonding:

respectively coating the nano metal slurry on a template on which a transition layer metal/gold composite metal coating is deposited and the surface of one side of a diamond sheet on which the transition layer metal/gold composite metal coating is deposited, preserving heat for 30-60 min at the temperature of 120-160 ℃, then aligning and bonding, and preserving heat for 0.5-1 h at the temperature of 180-280 ℃ and under the condition that the surface applied pressure is not less than 20MPa to obtain a material after hot-pressing sintering bonding;

thirdly, stripping the template and keeping the metal layer on the diamond:

dipping the material subjected to hot-pressing sintering bonding in a stripping solution, dissolving and stripping the template to obtain a diamond sheet with a nano metal layer and a transition layer metal/gold composite metal coating;

fourthly, surface activation cleaning:

cleaning and drying the diamond sheet with the nano metal layer and the transition layer metal/gold composite metal coating, and then carrying out argon plasma cleaning on the diamond sheet with the nano metal layer and the transition layer metal/gold composite metal coating and the semiconductor chip material with the transition layer metal/gold composite metal coating deposited to obtain a diamond sheet with a surface activated and cleaned and a semiconductor chip material with a surface activated and cleaned;

and V, bonding:

and (3) attaching the diamond sheet with the surface activated and cleaned and the semiconductor chip material with the surface activated and cleaned, and then transferring the diamond sheet and the semiconductor chip material into hot-pressing equipment for bonding connection to finish the surface smoothing and connection method of the diamond cooling fin.

The metal layer is not damaged in the stripping process of the third step of the specific test mode.

The principle is as follows:

(1) high roughness diamond bonded surface pre-smoothing technique. The technical difficulty and cost in the diamond polishing, cutting and bonding process are comprehensively considered, diamond with hundred-nanometer surface roughness is selected to be bonded with a semiconductor chip material, a sub-nanometer ultra-smooth metal surface diamond is simply manufactured by utilizing a one-step thin film transfer process based on nanometer metal template stripping, and then the diamond integrated packaging of a high thermal current device with low temperature, low cost and high reliability is realized through the bonding process.

(2) And the high-surface roughness diamond is bonded with the nano bonding of the heterogeneous material. In order to solve the problems of low reliability and high cost caused by high temperature, high vacuum, uniform coating and the like in the conventional bonding process, the nano bonding material comprises but is not limited to nano silver, nano copper and nano gold based on the characteristics of low-temperature sintering of nano particles at normal temperature and normal pressure, and the low-temperature, low-cost, low-porosity and low-thermal resistance bonding of diamond and heterogeneous materials is realized. The high compatibility with the front end and the rear end packaging procedures is realized while the heat dissipation benefit is ensured, and the integrated heat dissipation flip chip structure on the diamond sheet based on the nano bonding process is obtained.

The embodiment realizes the surface smoothing of the diamond with high surface roughness and the bonding connection with the high heat flux density unit at low temperature, low cost, high reliability and high compatibility, thereby realizing the reduction of the peak temperature of the high heat flux density unit in the using process and the temperature equalization among different areas.

The application scenario of the embodiment mainly includes high-power-density chips, modules and high-temperature parts of the packaging structure, and is used for rapidly achieving cooling and temperature equalization of peak hot spots in the area. The rapid cooling of local 'hot spots' is realized by using the diamond with high heat conductivity, and the temperature equalization is realized by using the characteristic of isotropic heat conduction of the diamond. Therefore, in order to better utilize the characteristics of the diamond material, the key points of the one-step film transfer smoothing process for stripping the nano metal template on the surface of the diamond and the subsequent bonding connection with materials such as silicon and the like are also the core to be solved by the invention, and a low-temperature, low-cost, vacuum-free and quick bonding connection scheme of the diamond and the silicon material is provided.

The beneficial effects of the embodiment are as follows:

the embodiment is based on a one-step smoothing method of film transfer, and provides a principle that high-quality bonding is realized between a diamond with large surface roughness and a semiconductor chip material by adopting nano metal, and sintering of nano metal particles in a low-temperature and normal-pressure atmospheric environment is realized, so that high-reliability bonding connection between the diamond and the semiconductor chip material is realized.

The technical scheme of the embodiment carries out rapid smoothing treatment on the diamond; and the subsequent surface activated metal diffusion bonding is combined, a high vacuum environment is not needed, the bonding of the diamond with large surface roughness (hundred nanometers) and the semiconductor chip material is realized, and the complexity and the cost of the prior art are reduced.

1. The one-step film transfer process based on the stripping of the nano metal template utilizes the densification transformation of nano metal particles in the process of pressure sintering to realize the smoothing treatment which is different from the prior art and needs to carry out high-precision polishing on diamond;

2. the subsequent metal diffusion bonding with surface activation is combined, because the gold has good stability and is not easy to be oxidized, high vacuum environment bonding is not needed, the problem of bonding rate reduction caused by long-time exposure of the surface to be bonded is solved, the bonding of diamond with large surface roughness (hundred nanometers) and a semiconductor chip material is realized, the final bonding temperature is not higher than 200 ℃, and the integration of the diamond and a flip chip is completed under the pressure of not more than 5 MPa. Compared with the conventional micro-nano metal sintering connection process, the bonding interface obtained by the method is thinner (5-30 microns) and more compact (the interface porosity is less than 10%), large-size connection is realized, and efficient heat dissipation of a semiconductor chip unit is facilitated.

The embodiment solves the key bonding problem in the process of enhancing the heat dissipation of the semiconductor chip by using the high-heat-conductivity diamond, and has wide applicability to the high-efficiency heat dissipation of devices with high heat flow density. The high-heat-density heat dissipation structure can be used for heat dissipation of applications with high heat-flow-density characteristics, such as SiC high-frequency devices, GaN power devices, optical communication modules, TR components for high-frequency communication and the like.

The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the template in the first step is a quartz plate with the roughness less than 1 nm; the semiconductor chip material in the first step is silicon, silicon carbide, gallium nitride or gallium oxide; the transition layer metal in the first step is one or more of Ti, Mo, Cr, Ni and W; the surface roughness of the diamond sheet in the first step is less than 1 micron. The rest is the same as the first embodiment.

The third concrete implementation mode: this embodiment is different from the first or second embodiment in that: and the cleaning in the step one is to sequentially use acetone and alcohol for ultrasonic cleaning for 5min to 10min, then use deionized water for washing, and finally dry. The other is the same as in the first or second embodiment.

The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: the argon plasma cleaning in the step one is to clean for 20 to 120 seconds under the conditions that the air pressure is 10 to 100Pa, the power is 100 to 200W and the argon flow is 20 to 60 sccm. The others are the same as the first to third embodiments.

The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: in the first step, a high-vacuum degree magnetron sputtering system is adopted to plate a transition layer metal layer of 10 nm-20 nm and a gold layer of 100 nm-200 nm on the template, the diamond sheet and the semiconductor chip material in sequence, and the method specifically comprises the following steps: keeping the target base distance at 80-100 mm, firstly vacuumizing to 5 × 10^-4Pa～10×10^-4Pa, starting under the conditions that the argon flow is 20 sccm-40 sccm, the radio frequency power supply power is 40W-60W and the pressure is 3 Pa-5 Pa, and then sequentially sputtering the transition layer metal layer and the gold layer under the conditions that the argon flow is 20 sccm-40 sccm, the radio frequency power supply power is 40W-60W and the pressure is 0.5 Pa-1 Pa. The rest is the same as the first to fourth embodiments.

The present embodiment performs sputtering using a target having a purity of not less than 99.995%.

The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: the mass percentage of the nano metal particles in the nano metal slurry in the step two is 80-90%; the nano metal particles are one or a mixture of several of nano silver, nano copper and nano gold. The rest is the same as the first to fifth embodiments.

The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: and step two, adopting ultrathin template printing, respectively coating the nanometer metal slurry on the template of the deposited transition layer metal/gold composite metal coating and the metal-coated side surface of the diamond sheet of the deposited transition layer metal/gold composite metal coating, wherein the coating thickness is 5-100 mu m. The others are the same as the first to sixth embodiments.

The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: the stripping solution in the third step is hydrofluoric acid solution with the mass percentage of 1-10%. The rest is the same as the first to seventh embodiments.

The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: the argon plasma cleaning in the fourth step is to clean 20 to 120s under the conditions that the air pressure is 10 to 100Pa, the power is 100 to 200W and the argon flow is 20 to 60 sccm. The other points are the same as those in the first to eighth embodiments.

The detailed implementation mode is ten: the present embodiment differs from one of the first to ninth embodiments in that: and step five, bonding connection is carried out for 10-30 min under the conditions that the pressure is less than or equal to 5MPa and the temperature is between room temperature and 200 ℃. The other points are the same as those in the first to ninth embodiments.

The following examples were used to demonstrate the beneficial effects of the present invention:

the first embodiment is as follows:

a surface smoothing and connecting method of a diamond cooling fin is carried out according to the following steps:

firstly, depositing a titanium/gold composite metal coating:

sequentially cleaning the template, the diamond sheet and the silicon bare chip and cleaning the template, the diamond sheet and the silicon bare chip by argon plasma, and then sequentially plating a titanium layer of 10nm and a gold layer of 150nm on the template, the diamond sheet and the silicon bare chip respectively by adopting a high-vacuum degree magnetron sputtering system to obtain the template on which the titanium/gold composite metal coating is deposited, the diamond sheet on which the titanium/gold composite metal coating is deposited and the silicon bare chip on which the titanium/gold composite metal coating is deposited;

coating nano metal slurry and hot-pressing sintering bonding:

respectively coating the nano metal slurry on a template deposited with the titanium/gold composite metal coating and the surface of one side of a diamond sheet deposited with the titanium/gold composite metal coating, preserving heat for 30min at the temperature of 140 ℃, then aligning and bonding, and preserving heat for 1h at the temperature of 275 ℃ and under the surface applied pressure of 30MPa to obtain a material subjected to hot-pressing sintering bonding;

thirdly, stripping the template and keeping the metal layer on the diamond:

dipping the material subjected to hot-pressing sintering bonding in a stripping solution, dissolving and stripping the template to obtain a diamond sheet with a nano metal layer and a titanium/gold composite metal coating;

fourthly, surface activation cleaning:

cleaning and drying the diamond sheet with the nano metal layer and the titanium/gold composite metal coating, and then carrying out argon plasma cleaning on the diamond sheet with the nano metal layer and the titanium/gold composite metal coating and the silicon bare chip with the titanium/gold composite metal coating deposited thereon to obtain a diamond sheet with a surface activated and cleaned surface and a silicon bare chip with a surface activated and cleaned surface;

and V, bonding:

and (3) attaching the diamond sheet with the surface activated and cleaned and the silicon bare chip with the surface activated and cleaned, and then transferring the diamond sheet and the silicon bare chip into hot-pressing equipment for bonding connection to obtain a bonding material of the diamond and the silicon bare chip, thereby finishing the surface smoothing and connection method of the diamond heat sink.

The template in the first step is a quartz plate with the roughness less than 1nm, and the size is 15mm multiplied by 0.4 mm; the diamond sheet in the step one has the size of 10mm multiplied by 0.4mm, and the surface roughness is about 100 nm; the size of the silicon bare chip in the first step is 10mm multiplied by 0.4mm, and the surface roughness is less than 2 nm.

And the cleaning in the step one is to sequentially use acetone and alcohol for ultrasonic cleaning for 10min, then use deionized water for washing, and finally dry for 30min at the temperature of 50 ℃.

The argon plasma cleaning in the first step is specifically to clean for 60s under the conditions that the air pressure is 50Pa, the power is 200W and the argon flow is 20 sccm.

In the first step, a high-vacuum degree magnetron sputtering system is adopted to plate a titanium layer of 10nm and a gold layer of 150nm on the template, the diamond sheet and the silicon die in sequence, and the method specifically comprises the following steps: keeping the target base distance at 80mm, and vacuumizing to 5 × 10^-4Pa, starting under the conditions that the argon flow is 20sccm, the radio frequency power supply power is 60W and the pressure is 3Pa, and sputtering a titanium layer and a gold layer in sequence under the conditions that the argon flow is 20sccm, the radio frequency power supply power is 60W and the pressure is 0.5 Pa.

The mass percentage of the nano metal particles in the nano metal slurry in the step two is 85 percent; the nano metal particles are nano silver;

and step two, adopting ultrathin template printing, respectively coating the nanometer metal slurry on the surface of one side of the template deposited with the titanium/gold composite metal coating and the surface of one side of the diamond sheet deposited with the titanium/gold composite metal coating, wherein the coating thickness is 15 micrometers.

The stripping solution in the third step is a hydrofluoric acid solution with the mass percentage of 3%.

The argon plasma cleaning in the fourth step is to clean for 60s under the conditions that the air pressure is 50Pa, the power is 100W and the argon flow is 20 sccm.

The cleaning described in step four is rinsed several times with deionized water.

And step five, bonding connection is carried out for 30min under the condition that the pressure is 5MPa and the room temperature is reached.

Example two: the difference between the present embodiment and the first embodiment is: in the first step, a high-vacuum degree magnetron sputtering system is adopted to sequentially plate a chromium layer of 10nm and a gold layer of 100nm on the template, the diamond sheet and the silicon die respectively; in the second step, under the conditions that the temperature is 230 ℃ and the surface applied pressure is 30MPa, the heat is preserved for 1h to obtain a material after hot-pressing sintering bonding; and step five, bonding and connecting for 30min under the conditions that the pressure is 3MPa and the temperature is 120 ℃. The rest is the same as the first embodiment.

Fig. 2 is atomic force scanning microscope images before and after smoothing of the diamond surface, (a) is a 50 μm × 50 μm area scanning image of the original diamond wafer, (b) is a 50 μm × 50 μm area scanning image of the diamond wafer with the nano-metal layer and the chromium/gold composite metal coating left in the third step of the example, (c) is a 5 μm × 5 μm area scanning image of the original diamond wafer, and (d) is a 5 μm × 5 μm area scanning image of the diamond wafer with the nano-metal layer and the chromium/gold composite metal coating left in the third step of the example. Fig. 3 is a roughness contrast graph, (a) is a 50 μm × 50 μm area scan picture of an original diamond plate, (b) is a 50 μm × 50 μm area scan picture of a diamond plate left with a nano-metal layer and a chromium/gold composite metal plating layer in the third example step, (c) is a 5 μm × 5 μm area scan picture of an original diamond plate, and (d) is a 5 μm × 5 μm area scan picture of a diamond plate left with a nano-metal layer and a chromium/gold composite metal plating layer in the third example step. As can be seen from the figure, the original surface roughness of the diamond is about 100nm, and the surface roughness is reduced to a few nanometers after the smoothing treatment of the embodiment, so that the requirement of subsequent metal bonding is met.

FIG. 4 is a scanning electron microscope image of the diamond-silicon die bonding material interface prepared in example two; FIG. 5 is a calculated plot of porosity for the interface section of FIG. 4; the diamond to silicon die interface bonds well, with a total bond layer thickness of about 14 μm, and a cross-sectional porosity of about 8.57% as seen by image analysis software.

FIG. 6 is an atomic force scanning microscope photograph of a diamond before and after smoothing of a diamond surface, (a) is a 50 μm × 50 μm area scanning photograph of an original diamond piece, (b) is a 50 μm × 50 μm area scanning photograph of a diamond piece left with a nano metal layer and a titanium/gold composite metal plating layer in one step of the example, (c) is a 5 μm × 5 μm area scanning photograph of an original diamond piece, and (d) is a 5 μm × 5 μm area scanning photograph of a diamond piece left with a nano metal layer and a titanium/gold composite metal plating layer in one step of the example; fig. 7 is a roughness contrast graph, (a) is a 50 μm × 50 μm area scan picture of an original diamond wafer, (b) is a 50 μm × 50 μm area scan picture of a diamond wafer with a nanometal layer and a titanium/gold composite metal coating left in the third step of the example, (c) is a 5 μm × 5 μm area scan picture of an original diamond wafer, and (d) is a 5 μm × 5 μm area scan picture of a diamond wafer with a nanometal layer and a titanium/gold composite metal coating left in the third step of the example. As can be seen from the figure, the original surface roughness of the diamond is about 100nm, and the surface roughness is reduced to a few nanometers after the smoothing treatment of the embodiment, so that the requirement of subsequent metal bonding is met.

FIG. 8 is a scanning electron microscope image of the diamond-silicon die bonding material interface prepared according to the first example; FIG. 9 is a calculated plot of porosity for the interface section of FIG. 8; the diamond to silicon die interface bonds well, with a total bond layer thickness of about 14 μm, and a cross-sectional porosity of about 8.52% as seen by image analysis software.

FIG. 10 is a schematic diagram showing the principle of a diamond-silicon die bonding strength thrust test, in which a diamond-silicon die bonding sample is bonded to a test base by a strong adhesive, and is tightly attached to a side wall of the diamond by a push-type broach, so as to keep a distance of 15 μm from the bottom, and a horizontal thrust is applied at 1mm/min until a bonding interface is damaged; FIG. 11 is a graph comparing the thrust test strength of diamond to silicon die bonded samples; it can be seen that the overall thrust test strength is greater than 8MPa, showing good bonding strength.