A method for ultra-high temperature resistant hermetic packaging

Abstract

The present invention relates to the technical field of thermocompression bonding in microelectronic packaging, and specifically to a method for hermetic packaging resistant to ultra-high temperatures, which includes the following steps: platinum metal is used as the bonding connection material for bonding, and the bonding material is not mixed with other metal materials; first, the substrate bottom film is cleaned, and then a dielectric layer is prepared by chemical vapor deposition; a bottom electrode is prepared through photolithography, sputtering, and stripping; a nano-platinum column array is fabricated on the surface of the bonding bump platinum metal by a deposition method; then the substrate is immersed in a hexanethiol solution to self-assemble a barrier film to prevent oxidation of the platinum metal surface, and finally, individual microstructures are separated by laser scribing; two structures with sealing rings and bonding bumps are placed in a flip-chip bonder, and after automatic alignment, heating, and pressurization by the bonder, bonding is started, and finally the two structures are combined together. The present invention can provide an oxygen-free and high-temperature protection for graphene nano-film materials at about 1500 °C by directly bonding Pt-Pt to form an oxygen-free vacuum cavity.

Description

Technical Field

[0001] The present invention relates to the technical field of thermocompression bonding in microelectronic packaging, and specifically to a hermetic packaging method suitable for microelectronics that can withstand ultra-high temperatures. Background Art

[0002] With the continuous upgrading of aeroengines and gas turbines in recent years, the temperatures they can withstand have gradually increased. The operating temperatures of some key components of these devices, such as turbine blades and combustion chambers, reach over 1000°C. Under such operating temperatures, the high-temperature resistance required by temperature sensors has gradually become an improvement index. Using temperature sensors to perform real-time temperature detection can effectively analyze the fatigue degree of the devices, which is important for detecting device fatigue. It can also record temperature changes and improve the combustion efficiency of the engine.

[0003] With the development of microelectronic sensors, since monolayer graphene was successfully separated from graphite by the micromechanical cleavage method in 2004, the technology for fabricating graphene has developed rapidly. Due to the excellent electrical conductivity of graphene, using graphene to fabricate microelectronic sensors has become a trend.

[0004] In recent years, the technology for fabricating graphene has become increasingly mature. High-temperature environment sensors based on graphene are widely used in various fields such as aerospace, medicine, and metallurgy. With the continuous update of packaging requirements, people have continuously updated traditional bonding materials to adapt to the new environment.

[0005] The essence of bonding is the mutual diffusion of atoms on the surfaces of two metals. Since a thin oxide film will form on the surface of the metal in air, this oxide film blocks the mutual diffusion of atoms on the surfaces of the two metals. Therefore, the diffusion of atoms on the metal surface cannot occur unconditionally.

[0006] For diffusion-driven thermocompression bonding, the mutual diffusion of atoms at the bonding interface is the essence for the bonding to be achieved. Gustav Tammann found that as the temperature rises, the amplitude of atoms / ions near the equilibrium position becomes larger and larger, and atoms / ions leave the equilibrium position, enhancing diffusion. And the temperature at which atoms / ions start to exhibit significant diffusion effects (Tammann temperature) is usually much lower than the melting point of the material or the eutectic temperature of the system. For metal materials, the Tammann temperature (t B ) and its melting point (t m ) have the following relationship:

[0007] t B =(0.3 - 0.4)t m

[0008] According to the above relationship, the Tamman temperature of Pt can be obtained as 531.6 - 708.8 °C (Pt melting point: 1772 °C). When the bonding temperature exceeds the above temperature range, the atomic diffusion at the bonding interface will be significantly enhanced.

[0009] Since Pt is not easily oxidized compared with other metal materials, during bonding, it is not necessary to coat the platinum surface with a passivation layer. Only by performing an activation treatment on the Pt bonding surface can the Pt on the bonding surface be diffused. This design mainly uses a dry method to activate the bonding platinum surface.

[0010] According to the Tamman temperature of metal materials, if each material is directly bonded without treatment, a very high temperature is required, which not only easily damages the device but also greatly increases the manufacturing cost and is not conducive to mass production. Therefore, generally, the bonding surface needs to be treated accordingly before bonding. Generally, there are two types of methods to remove the oxide film on the interface surface. One is to pass a certain power of plasma gas such as argon on the metal surface, which is commonly known as the dry method; the other is to place the metal surface in a reducing solution to remove the surface oxide film, which is commonly known as the wet method. Among the surface treatment methods, the dry method is easy to perform and has a certain effect on reducing the bonding temperature during the bonding process.

[0011] However, the dry method cannot completely remove the oxide film on the bonding surface. Especially for those metal materials that are prone to form a dense oxide film on the surface, the effect is relatively small. Although the wet method can remove the surface oxide film through chemical reactions, it is relatively difficult to operate, and the bonding in the liquid is greatly affected by irrelevant factors. Summary of the Invention

[0012] The present invention combines the self-assembled monolayer (SAM) low-temperature bonding process and the nanoparticle low-temperature bonding process to reduce the temperature during platinum-platinum bonding, so that the bonded device has good ultra-high temperature resistance and airtightness. The advantage of the present invention is to utilize the existing process to improve the bonding efficiency, and the bonding quality is reliable, which can be widely used in production.

[0013] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0014] An ultra-high temperature resistant and airtight packaging method, comprising the following steps:

[0015] S1. During bonding, platinum metal is used as the bonding connection material, and no other metal materials are mixed in the bonding material;

[0016] S2. First, clean the substrate bottom film, and then prepare a dielectric layer by chemical vapor deposition;

[0017] S3. Prepare the bottom electrode through photolithography, sputtering, and stripping;

[0018] S4. Use the deposition method to fabricate a nano-platinum column array on the surface of the bonding bump platinum metal;

[0019] S5. Then immerse the substrate into the hexanethiol solution to self-assemble a barrier film to prevent the oxidation of the platinum metal surface, and finally separate the individual microstructures by means of laser scribing;

[0020] S6. Place the two structures with sealing rings and bonding bumps into a flip-chip bonder. After the bonder automatically aligns, heats, and pressurizes, the bonding starts, and finally the two structures are combined together.

[0021] The substrate is made of sapphire Al 2 O 3 , silicon or silicon dioxide; the dielectric layer material comprises an insulating layer prepared from SiN X , SiO 2 materials with a thickness of 10 - 100 nm.

[0022] The bottom electrode is prepared by using a mask pattern, a sealing ring containing microelectronic structures or for a graphene high-temperature sensor.

[0023] The adhesion layer sputtered during the preparation of the bottom electrode contains two metal materials, Cr and Ti, with a coating thickness of 50 - 100 nm and a power of 1 kW.

[0024] The thickness of the sputtered layer is between 300 - 500 nm.

[0025] The nano process for the bonding surface adopts a column array, spherical, particulate or porous process.

[0026] A layer of alkanethiol is self-assembled on the surface of the substrate, and the method for assembling the layer of alkanethiol adopts a wet method or a vapor deposition method.

[0027] The bonding method adopts direct thermocompression bonding. The direct thermocompression bonding includes surface activation treatment, heating, and pressurization, and the direct thermocompression bonding uses a flip-chip bonder.

[0028] The surface activation treatment method is a dry method. The dry method is to use Ar 2 or H 2 gas to treat the oxide film on the bonding surface to achieve the purpose of activation.

[0029] The gas power of the surface activation treatment is within 200 W - 400 W, and the time of the surface activation treatment within 10 s - 600 s is within the scope of the claims; the annealing temperature of the direct thermocompression bonding is 200 - 700 °C, and the annealing time of the direct thermocompression bonding is 10 min - 60 min; the pressure applied during annealing in the direct thermocompression bonding ranges between 20 - 120 Mpa, and the time for applying the pressure during annealing is between 10 min - 60 min.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This encapsulation method has great advantages compared with the technology described in the background. By directly bonding Pt-Pt to form an oxygen-free vacuum cavity, it can provide oxygen-free and high-temperature protection for graphene nanomembrane materials at about 1500°C. This encapsulation method is simple and easy to implement, and the encapsulation structure is reasonable and reliable, suitable for many high-temperature environment monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a cell structure diagram of a mask plate according to an embodiment of the present invention;

[0033] Figure 2 It is a shape diagram of a single repeating structure of a cell according to an embodiment of the present invention;

[0034] Figure 3 It is a schematic side view of a bonding substrate with a bottom electrode prepared, where Cr is an adhesion metal layer, which helps prevent the Pt layer from peeling off.

[0035] Figure 4 It is a schematic diagram of growing a nano-platinum column array on a bonding bump;

[0036] Figure 5 It is a schematic diagram of self-assembling a layer of alkane thiol on the surface of a platinum-plated sheet;

[0037] Figure 6 It is a schematic diagram of the thermal detachment of alkanethiol hydrogen self-assembled on the platinum surface during bonding.

[0038] Figure 7 It is a schematic diagram of the bonding process of a clean platinum column array under the action of hot pressing after the thermal detachment of alkanethiol hydrogen self-assembled on the platinum surface. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0040] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0041] The present invention will be further described below with reference to the accompanying drawings:

[0042] As Figure 1 shown, the implementation of the present invention is based on the structure in the figure. The structure in the figure is a photolithography mask plate, which is composed of a total of 4x4 individual structures to form a square cell with a length of 5 mm and a width of 5 mm. Its function is to prepare electrode patterns on the substrate, namely the sealing ring and the bonding bumps. Since the minimum dimension of thermocompression bonding is 5 mm, when bonding, it is a whole cell that is bonded.

[0043] Figure 2 Shown is the specific dimensional structure of each unit. Among them, the side length of the square bonding bump is 160 μm, and the width of the sealing ring is 80 μm. The outer width of the square sealing ring is 1.31 mm, the inner width is 1.15 mm, and the outer margin of the bonding bump from the inner side of the square sealing ring is 160 μm. The sealing ring plays a role in forming a structure with a certain airtightness inside after bonding.

[0044] After the mask plate is manufactured, the following are the specific steps for preparing the bonding structure:

[0045] 1. Wafer preparation: Sapphire (Al 2 O 3 )

[0046] 2. Cleaning: Conventional cleaning; ultrasonically cleaning with acetone, isopropanol, and water in sequence, and N 2 blowing dry

[0047] 3. Preparation of the bottom electrode

[0048] The preparation of the bottom electrode is divided into 3 steps: photolithography, sputtering, and stripping.

[0049] (1) Photolithography: Photolithography is an important step in preparing the bottom electrode. The pattern and size of the electrode on the substrate are lithographed onto the substrate through the mask plate. Where there is a mask plate, ultraviolet light is blocked and the photoresist is not affected. Where there is no mask plate, the photoresist absorbs ultraviolet light and falls off with the developer, forming an electrode pattern.

[0050] (2) Sputtering: After lithography, the substrate forms a bottom electrode pattern with the photoresist as a template. Using this pattern as the coating substrate, select the LB--18 sputtering platform to magnetron sputter the Cr / Pt layer, with Cr 50 nm - 1 kW and Pt 300 nm - 0.2 kW.

[0051] (3) Lift-off: For the substrate sputtered with the Cr / Pt layer, through negative photoresist lift-off, dissolve the Cr / Pt layer plated on the photoresist. Dissolution method: Avoid ultrasonic waves, natural lift-off, soak in acetone. After lift-off, the Cr / Pt layer directly plated on the substrate remains, which is the bottom electrode pattern we need, and the size is completed.

[0052] 4. Deposition method: Fabricate a nano-platinum pillar array on the surface of the bonding bump platinum metal through the deposition method.

[0053] 5. Surface activation: After fabricating the nano-platinum pillar array, pass Ar gas for surface activation to remove the surface oxide film and improve the surface activation performance.

[0054] 6. Chemical vapor deposition method: Immediately after surface activation, deposit a layer of alkanethiol hydrogen film on the surface of the substrate by chemical vapor deposition to prevent the bonding surface from being oxidized again.

[0055] 7. Dicing: There is more than one structural unit fabricated on a silicon wafer, and they are neatly arranged on the silicon wafer. Generally, the fabricated silicon wafer units are separated by mechanical dicing. For substrates with higher hardness, such as sapphire (Al 2 O 3 ) substrates, use laser dicing to separate each structural unit.

[0056] 8. Bonding: Use an automatic alignment flip-chip bonder to directly thermocompress to bond the upper and lower substrates together.

[0057] Example 1

[0058] The specific process steps of this packaging method include:

[0059] Wafer preparation: The sapphire (Al 2 O 3 ) has a size of 2 inches and 400 μm.

[0060] Cleaning: Conventional cleaning; ultrasonically clean with acetone, isopropanol, and water for 5 minutes in sequence, and then N 2 blow dry.

[0061] Sputtering: Deposit a layer of Cr as an adhesion layer on the clean sapphire (Al 2 O 3 ) substrate. Select the LB--18 sputtering platform to magnetron sputter the Cr layer. The thickness of the Cr layer is 50 nm, and the sputtering power is 1 kW.

[0062] Bottom electrode: Preparation of the bottom electrode; It is divided into 3 steps: photolithography, sputtering, and stripping.

[0063] Photolithography: Select Figure 1 the mask plate shown, perform photolithography on the substrate with photoresist attached. After photolithography, pre-bake at 150 °C for 60 s using a hot plate, expose with MA6 for 7.0 s (hard contact); perform mid-bake at 100 °C for 60 s using a hot plate; use NMD-3 developer to remove the photoresist. The time is 17 s.

[0064] Sputtering: After photolithography, select the LB--18 sputtering platform and magnetron sputter the Pt layer. The thickness of the Pt layer is 300 nm and the sputtering power is 0.2 kW.

[0065] Stripping: For the substrate sputtered with the Cr / Pt layer, dissolve the Cr / Pt layer plated on the photoresist through negative photoresist stripping. The dissolution method is to avoid ultrasonic waves, natural stripping, and acetone immersion.

[0066] Deposition: Fabricate a nano-platinum column array on the surface of the bonding bump platinum metal through the deposition method. The diameter of the nano-copper column is 10 nm and the length is 300 nm.

[0067] Surface activation: After fabricating the nano-platinum column array, perform surface activation by passing Ar gas. The Ar passing power is 400 W and the treatment time is 300 s to remove the surface oxide film and improve the surface activation performance.

[0068] Immersion: Immediately immerse the surface-activated substrate in a hexanethiol solution for 2 h, take it out and 2 dry it with air for about 5 min to prevent the bonding surface from being oxidized again.

[0069] Dicing: Use the method of laser dicing to separate each structural unit.

[0070] Bonding: Place the fabricated symmetric upper and lower substrates into an FC150 flip-chip bonder. After automatic alignment by the flip-chip bonder, anneal at 10 MPa and 200 - 400 °C for about 30 min to complete the bonding, as Figure 7 shown.

[0071] Only the preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A method for hermetic packaging resistant to ultra-high temperature, characterized in that: It includes the following steps: S1. Use platinum metal as the bonding connection material for bonding, and the bonding material does not mix with other metal materials; S2. First clean the substrate bottom film, and then prepare the dielectric layer by chemical vapor deposition; S3. Prepare the bottom electrode through photolithography, sputtering, and stripping; S4. Use the deposition method to fabricate a nano-platinum column array on the surface of the bonding bump platinum metal; S5. Then immerse the substrate in a hexanethiol solution to self-assemble a barrier film to prevent oxidation of the platinum metal surface, and finally separate the individual microstructures by laser scribing; S6. Place two structures with sealing rings and bonding bumps into a flip-chip bonder. After the bonder automatically aligns, heats, and pressurizes, bonding starts, and finally the two structures are combined together; The substrate is made of sapphire Al 2 O 3 , silicon or silicon dioxide; the dielectric layer material includes an insulating layer made of 10-100 nm of SiN X , SiO 2 material; The bonding method uses direct thermocompression bonding. The direct thermocompression bonding includes surface activation treatment, heating, and pressurization. The direct thermocompression bonding uses a flip-chip bonder; The surface activation treatment method is a dry process, and the dry process uses Ar gas with a power of 200W - 400W 2 or H 2 gas to treat the oxide film on the bonding surface to achieve the purpose of activation.

2. A method for hermetic packaging resistant to ultra-high temperature according to claim 1, characterized in that: The preparation of the bottom electrode uses a mask pattern, a sealing ring containing microelectronic structures, or for a graphene high-temperature sensor.

3. A method for hermetic packaging resistant to ultra-high temperature according to claim 1, characterized in that: The adhesion layer sputtered during the preparation of the bottom electrode contains two metal materials, Cr and Ti, the coating thickness is 50 - 100 nm, and the power is 1 kW.

4. A method for hermetic packaging resistant to ultra-high temperature according to claim 1, characterized in that: The thickness of the sputtered layer is between 300 - 500 nm.

5. A method for hermetic packaging resistant to ultra-high temperature according to claim 1, characterized in that: The surface nano-process of the bonding uses a column array, spherical, particulate, or porous process.

6. A method for hermetic packaging resistant to ultra-high temperature according to claim 1, characterized in that: A layer of alkanethiol is self-assembled on the surface of the substrate, and the method for assembling a layer of alkanethiol uses a wet method or chemical vapor deposition.

7. A method for hermetic packaging resistant to ultra-high temperature according to claim 1, characterized in that: The time of the surface activation treatment is 10 s - 600 s; the annealing temperature of the direct thermocompression bonding is 200 - 700 °C, and the annealing time of the direct thermocompression bonding is 10 min - 60 min; the pressure applied during annealing in the direct thermocompression bonding ranges from 20 - 120 Mpa, and the time for applying pressure during annealing is between 10 min - 60 min.

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