A method for fabricating metal circuits on a ceramic substrate

Abstract

This invention relates to a method for fabricating metal circuits on a ceramic substrate. The method involves surface treatment of aluminum nitride ceramics, selection of transition layers, and preparation of the crystal orientation of the metal layers. By fabricating a multilayer structure of insulating oxides, conductive oxides, and conductive metal layers, and introducing a Cu(111) layer, the conductivity of the thin-layer metal is enhanced. The method includes the following steps: Step 1: Cleaning the aluminum nitride ceramic substrate blank with nitric acid and / or deionized water, and performing a chemical reaction in an HF solution of appropriate concentration and at a heating temperature of appropriate degrees Celsius for a corresponding time period to prepare a buffer layer; Step 2: Preparing a multilayer structure of conductive oxides and / or conductive metal layers by magnetron sputtering; Step 3: After completing Step 2, photolithography is applied to the ceramic substrate to form a circuit pattern; Step 4: Electroplating the patterned circuit on the ceramic substrate to form an electrical connection surface layer; Step 5: Annealing the ceramic substrate after Step 4.

Description

Technical Field

[0001] This invention relates to a method for fabricating metal circuits, specifically a method for fabricating metal circuits on a ceramic substrate. Background Technology

[0002] Ceramic substrates are increasingly widely used in electronic packaging, especially in power electronic devices such as IGBTs (Insulated Gate Bipolar Transistors), LDs (Laser Diodes), high-power LEDs (Light Emitting Diodes), CPVs (Central Photovoltaics), and sensor packaging, due to their excellent thermal conductivity, heat resistance, insulation, low coefficient of thermal expansion, and continuously decreasing cost.

[0003] In terms of structure and manufacturing process, ceramic substrates can be further divided into HTCC, LTCC, TFC, DBC, DPC, etc. Among them, except for DPC, due to the characteristics of the process, the fabrication of metal circuits is often not very precise, which cannot meet the precision requirements for device packaging with high integration or special applications.

[0004] DPC fabrication begins with pretreatment and cleaning of the ceramic substrate. A metal layer is then deposited on the substrate surface as a seed layer using vacuum sputtering. Next, photolithography, development, and etching processes are used to fabricate the circuitry. Finally, electroplating / chemical plating is used to increase the circuit thickness. After the photoresist is removed, the substrate fabrication is complete. The introduction of semiconductor chip technology brings advantages to DPC processes, including the use of thin-film and photolithography techniques, resulting in finer metal lines on the substrate. Therefore, DPC substrates are ideal for packaging electronic devices with high alignment precision requirements.

[0005] However, DPC substrates also have some shortcomings: the thickness of the electroplated copper layer is limited, and the electroplating wastewater causes significant pollution; the bonding strength between the metal layer and the ceramic is low, resulting in low reliability in product applications. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating metal circuits on ceramic substrates. By surface treatment of aluminum nitride ceramics, selection of transition layers and preparation of special crystal orientation of metal layers, a multilayer structure of insulating oxide-conductive oxide-metal conductive layer is prepared to improve the weak bonding force caused by direct sputtering of metal circuits. At the same time, the preparation of Cu(111) layer is introduced to enhance the conductivity of thin-layer metal.

[0007] The objective of this invention is achieved as follows:

[0008] A method for fabricating metal circuits on a ceramic substrate includes surface treatment of aluminum nitride ceramic, selection of transition layers, and preparation of the crystal orientation of the metal layer. This involves fabricating a multilayer structure of insulating oxide, conductive oxide, and conductive metal layers, and introducing a Cu(111) layer to enhance the conductivity of the thin-layer metal. The method comprises the following steps:

[0009] Step 1: Clean the aluminum nitride ceramic substrate blank with nitric acid and / or deionized water, and carry out a chemical reaction in an HF solution of appropriate concentration and at a heating temperature of appropriate degrees Celsius for an appropriate time period to prepare a buffer layer.

[0010] Step 2: Prepare a multilayer structure of conductive oxide and / or metal conductive layers by magnetron sputtering;

[0011] Step 3: After completing Step 2, the ceramic substrate is then patterned using photoresist to form a circuit pattern.

[0012] Step 4: Electroplating is performed on the patterned circuitry on the ceramic substrate to form an electrical connection surface layer;

[0013] Step 5: Anneal the ceramic substrate after completing Step 4.

[0014] The method for fabricating metal circuits on a ceramic substrate according to claim 1 is characterized in that: in step one, an AlF buffer layer is prepared by reacting in a 1%-3% HF solution and under heating conditions of 50℃-70℃ for 25s-35s, serving as an intermediate buffer layer, especially as a metal layer platform formed after patterning etching. The AlF buffer layer blocks the conduction of heat from the power device and reduces the expansion scale of the metal layer.

[0015] The thickness of the buffer layer is 1 nm - 5 nm.

[0016] In step two, after cleaning the ceramic substrate blank from step one, the ceramic substrate enters the magnetron sputtering cavity; an alumina film and / or a zinc oxide film and / or a Ni film and / or a Cu film and / or a NiAu film are prepared by magnetron sputtering.

[0017] The thickness of the alumina film is 10 nm - 20 nm; the thickness of the Ni film is 5 nm - 10 nm; and the thickness of the NiAu film is 10-20 nm.

[0018] The thickness of the zinc oxide film is 100-200 nm, and the magnetron sputtering temperature for preparing the zinc oxide film is 290℃-310℃.

[0019] The Cu film has a thickness of 240 nm - 1000 nm and a crystal orientation of (111). The magnetron sputtering temperature for preparing the Cu film is 18℃-24℃, and the magnetron sputtering vacuum is 6×10⁻⁶. -3Torr, argon flow rate of magnetron sputtering 8 sccm - 12 sccm, magnetron sputtering time of 3500 s - 3700 s, magnetron sputtering speed of 0.2 nm / s - 0.4 nm / s, magnetron sputtering substrate rotation speed of 20 r / min - 35 r / min, sputtering to prepare Cu film, conductive layer with crystal orientation (111), reducing equivalent resistance and improving current efficiency within a limited conductive layer thickness range.

[0020] After completing step two, the ceramic substrate is patterned by photolithography with photoresist, and the Cu film and ZnO film layers are etched by wet etching, and the alumina film layer is etched by dry etching, so as to form a circuit pattern on the ceramic substrate.

[0021] After completing step three, the ceramic substrate is electroplated with gold with a thickness of 90 nm - 110 nm to form an electrical connection surface layer on the ceramic substrate.

[0022] The ceramic substrate forming the electrical connection surface layer is annealed to form a composite layer of aluminum nitride, aluminum fluoride, and aluminum oxide; and an intermediate layer of NiO film and CuO film is formed between the ZnO film, Ni film, Cu film, and Ni film; the annealing temperature is 100℃-900℃ or 300℃-600℃.

[0023] The beneficial effects of this invention are as follows:

[0024] By introducing an oxide intermediate layer and using annealing to achieve the fusion of cross-sections of different materials, the bonding force between the metal circuit and the ceramic substrate is improved.

[0025] By magnetron sputtering a ZnO seed layer and sputtering a Cu(111) conductive layer thereon, the equivalent resistance is reduced and the current efficiency is improved within a limited conductive layer thickness range. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the welding pull force of the sputtered metal film in an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of the XRD diffraction intensity of sputtered Cu films on different seed layers in an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the sheet resistance and volume resistance of copper films of different thicknesses in an embodiment of the present invention.

[0029] Figure 4 This is a schematic diagram of the surface electron concentration and bulk electron concentration of the ceramic substrate in an embodiment of the present invention.

[0030] Figure 5 This is a schematic diagram of the structure of the ceramic substrate before annealing in an embodiment of the present invention.

[0031] Figure 6 This is a schematic diagram of the structure of the ceramic substrate after annealing in an embodiment of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] See Figures 1-6 A method for fabricating metal circuits on a ceramic substrate includes surface treatment of aluminum nitride ceramic, selection of transition layers, and preparation of the crystal orientation of the metal layer. This is achieved by fabricating a multilayer structure of insulating oxide, conductive oxide, and conductive metal layers, and by introducing a Cu(111) layer to enhance the conductivity of the thin-layer metal. The method comprises the following steps:

[0034] Step 1: Clean the aluminum nitride ceramic substrate blank with nitric acid and / or deionized water, and carry out a chemical reaction in an HF solution of appropriate concentration and at a heating temperature of appropriate degrees Celsius for an appropriate time period to prepare a buffer layer.

[0035] Step 2: Prepare a multilayer structure of conductive oxide and / or metal conductive layers by magnetron sputtering;

[0036] Step 3: After completing Step 2, the ceramic substrate is then patterned using photoresist to form a circuit pattern.

[0037] Step 4: Electroplating is performed on the patterned circuitry on the ceramic substrate to form an electrical connection surface layer;

[0038] Step 5: Anneal the ceramic substrate after completing Step 4.

[0039] According to the method for fabricating metal circuits on a ceramic substrate as described in claim 1, the AlF buffer layer is prepared by reacting in a 1%-3% HF solution and under heating conditions of 50℃-70℃ for 25s-35s.

[0040] The thickness of the buffer layer is 1 nm - 5 nm.

[0041] In step two, after cleaning the ceramic substrate blank from step one, the ceramic substrate enters the magnetron sputtering cavity; an alumina film and / or a zinc oxide film and / or a Ni film and / or a Cu film and / or a NiAu film are prepared by magnetron sputtering.

[0042] The thickness of the alumina film is 10 nm - 20 nm; the thickness of the Ni film is 5 nm - 10 nm; and the thickness of the NiAu film is 10-20 nm.

[0043] The thickness of the zinc oxide film is 100-200 nm, and the magnetron sputtering temperature for preparing the zinc oxide film is 290℃-310℃.

[0044] The Cu film has a thickness of 240 nm - 1000 nm and a crystal orientation of (111). The magnetron sputtering temperature for preparing the Cu film is 18℃-24℃, and the magnetron sputtering vacuum is 6×10⁻⁶. -3 Torr, argon flow rate of magnetron sputtering 8 sccm - 12 sccm, magnetron sputtering time of 3500 s - 3700 s, magnetron sputtering speed of 0.2 nm / s - 0.4 nm / s, magnetron sputtering substrate rotation speed of 20 r / min - 35 r / min, sputtering to prepare Cu film, conductive layer with crystal orientation (111), reducing equivalent resistance and improving current efficiency within a limited conductive layer thickness range.

[0045] After completing step two, the ceramic substrate is patterned by photolithography with photoresist, and the Cu film and ZnO film layers are etched by wet etching, and the alumina film layer is etched by dry etching, so as to form a circuit pattern on the ceramic substrate.

[0046] After completing step three, the ceramic substrate is electroplated with gold with a thickness of 90 nm - 110 nm to form an electrical connection surface layer on the ceramic substrate.

[0047] The ceramic substrate forming the electrical connection surface layer is annealed to form a composite layer of aluminum nitride, aluminum fluoride, and aluminum oxide; and an intermediate layer of NiO film and CuO film is formed between the ZnO film, Ni film, Cu film, and Ni film; the annealing temperature is 100℃-900℃ or 300℃-600℃.

[0048] This method for fabricating metal circuits on ceramic substrates is a technological improvement aimed at enhancing aluminum nitride ceramic substrates, particularly for ceramic substrate circuits used in the sensor field.

[0049] The fabrication process of the metal circuit on this ceramic substrate is as follows:

[0050] After cleaning the aluminum nitride ceramic substrate blank with nitric acid and deionized water, it was reacted in a 1-3% HF solution at 60 degrees Celsius for 30 seconds to prepare an AlF buffer layer of 1-5 nm.

[0051] After the substrate blank is cleaned, the ceramic substrate enters the magnetron sputtering cavity;

[0052] Alumina films with a thickness of 10 nm to 20 nm were prepared on ceramic substrates by magnetron sputtering.

[0053] ZnO films with a thickness of 100 nm - 200 nm were prepared on ceramic substrates by magnetron sputtering at a temperature of 300 °C.

[0054] Ni films with a thickness of 5 nm to 10 nm were prepared on ceramic substrates by magnetron sputtering.

[0055] Cu films with a thickness of 240 nm - 1000 nm and a crystal orientation of (111) were prepared on ceramic substrates by magnetron sputtering; the magnetron sputtering temperature was room temperature; and the magnetron sputtering vacuum was 6 × 10⁻⁶. -3 Torr; argon flow rate for magnetron sputtering: 10 sccm; magnetron sputtering time: 3600 s; magnetron sputtering velocity: 0.3 nm / s; magnetron sputtering substrate rotation speed: 30 r / min;

[0056] NiAu films with a thickness of 10 nm to 20 nm were prepared on ceramic substrates by magnetron sputtering.

[0057] The ceramic substrate is patterned using photoresist photolithography; the Cu and ZnO layers are etched using wet etching, and the alumina layer is etched using dry etching.

[0058] The patterned circuit on the ceramic substrate is electroplated with 100nm gold to form an electrical connection surface layer.

[0059] After the ceramic substrate is removed, it undergoes high-temperature annealing to form a composite layer of aluminum nitride, aluminum fluoride, and aluminum oxide. An intermediate layer of NiO and CuO films is formed between the ZnO, Ni, and Cu films to improve interlayer adhesion. A schematic diagram of the metal circuit composite layer is shown below. Figure 5 , Figure 6 As shown.

[0060] During the relevant process, the decrease in thermal conductivity and the increase in thermal expansion coefficient of the oxide layer, as an intermediate buffer layer, especially the metal layer platform formed after patterning etching, block the conduction of heat from the power device and reduce the expansion scale of the metal layer.

[0061] After the ceramic substrate was prepared using this process, it was tested in actual tensile test samples using a 3.5mm × 3.5mm welding area. It can be seen that the maximum welding capacity exceeds 60N, which translates to a thrust of over 500g / mm², significantly improving the bonding strength between the metal and oxide. The ceramic substrate composite circuit layer of this invention exhibits significant effects, such as... Figure 1 As shown.

[0062] In the fabrication process of this scheme, various conductive intermediate layers were tested, as well as the crystal orientation selection of the metal layer fabricated on them. Figure 2The Cu(111) textures corresponding to sputtered copper films on different compound substrates are 86.9% for GaN, 91% for ZnO, and 81% for ITO. The corresponding grain sizes are 26.8 nm, 30 nm, and 20.8 nm, respectively. GaN exhibits a single-crystal structure, while ZnO grown by PECVD at 300°C has a hexagonal pyramidal structure with a certain single-crystal orientation, and ITO is a polycrystalline structure. It can be seen that a certain crystal orientation in the substrate facilitates the rapid alignment of the desired crystal orientation. The ZnO structure is most favorable for Cu(111) growth.

[0063] The Cu(111) films prepared above generally have a thickness exceeding 1 µm. Cu(111) nanotwins exhibit low interfacial energy at twin boundaries and weak electron scattering, thus showing better resistivity than nanocrystals, which are equivalent to coarse grains. To investigate the growth process of Cu films and the influence of different film thicknesses on texture and film formation efficiency, this section presents electrical properties and XRD tests on Cu films of different thicknesses. Figure 3 , 4 It can be observed that the sheet resistance abruptly changes when the film thickness is around 15-24 nm, indicating the formation of nanotwin grain boundaries. Simultaneously, the average grain size calculated by XRD is 20 nm, showing that the grains of copper layers thicker than 24 nm can connect to form a film. Upon increasing the thickness to over 240 nm, the Cu film is fully formed. At this point, the bulk resistance is 2.69 × 10⁻⁵ Ω / cm, approaching the bulk resistance. This achieves the same effect as a thick copper conductive layer with a thin film conductive layer.

[0064] The above describes the preferred embodiments of the present invention, illustrating and describing the basic principles, main features, and advantages of the invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a metal circuit on a ceramic substrate, characterized in that: The surface treatment of aluminum nitride ceramics, the selection of transition layers, and the preparation of the crystal orientation of the metal layer are carried out by preparing a multilayer structure of insulating oxide, conductive oxide, and metal conductive layer, and introducing the preparation of Cu(111) layer to improve the conductivity of the thin metal layer. The preparation steps include the following: Step 1: Clean the aluminum nitride ceramic substrate blank with nitric acid and / or deionized water, and carry out a chemical reaction in an HF solution of appropriate concentration and at a heating temperature of appropriate degrees Celsius for an appropriate time period to prepare a buffer layer. Step 2: Prepare a multilayer structure of conductive oxide and / or metal conductive layers by magnetron sputtering; Step 3: After completing Step 2, the ceramic substrate is then patterned using photoresist to form a circuit pattern. Step 4: Electroplating is performed on the patterned circuitry on the ceramic substrate to form an electrical connection surface layer; Step 5: Anneal the ceramic substrate after completing Step 4; In step one, an AlF buffer layer is prepared by reacting in a 1%-3% HF solution and under heating conditions of 50℃-70℃ for 25s-35s. In step two, after cleaning the ceramic substrate blank from step one, the ceramic substrate enters the magnetron sputtering cavity; aluminum oxide film, zinc oxide film, Ni film, Cu film, and NiAu film are prepared by magnetron sputtering. The thickness of the alumina film is 10 nm - 20 nm; the thickness of the Ni film is 5 nm - 10 nm; the thickness of the NiAu film is 10-20 nm. The thickness of the zinc oxide film is 100-200 nm, and the magnetron sputtering temperature for preparing the zinc oxide film is 290℃-310℃; The Cu film has a thickness of 240 nm - 1000 nm and a crystal orientation of (111). The magnetron sputtering temperature for preparing the Cu film is 18℃-24℃, and the magnetron sputtering vacuum is 6×10⁻⁶. -3 Torr, argon flow rate for magnetron sputtering 8 sccm - 12 sccm, magnetron sputtering time 3500 s - 3700 s, magnetron sputtering velocity 0.2 nm / s - 0.4 nm / s, and magnetron sputtering substrate rotation speed 20 r / min - 35 r / min; After completing step three, the ceramic substrate is electroplated with gold with a thickness of 90 nm - 110 nm to form an electrical connection surface layer on the ceramic substrate.

2. The method for fabricating a metal circuit on a ceramic substrate according to claim 1, characterized in that: The thickness of the buffer layer is 1 nm-5 nm.

3. The method for fabricating a metal circuit on a ceramic substrate according to claim 1, characterized in that: After completing step two, the ceramic substrate is patterned by photolithography with photoresist, and the Cu film and ZnO film layers are etched by wet etching, and the alumina film layer is etched by dry etching, so as to form a circuit pattern on the ceramic substrate.

4. The method for fabricating a metal circuit on a ceramic substrate according to claim 1, characterized in that: The ceramic substrate forming the electrical connection surface layer is annealed at a temperature of 100℃-900℃.

5. The method for fabricating a metal circuit on a ceramic substrate according to claim 1, characterized in that: The ceramic substrate forming the electrical connection surface layer is annealed at a temperature of 300℃-600℃.

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