Method for eliminating surface defects of aluminum oxide HTCC thick film mixed substrate

Abstract

According to the method for effectively repairing the inherent sunken part on the surface of the aluminum oxide HTCC thick film mixed substrate, the surface of the aluminum oxide HTCC substrate is subjected to film deposition and then is subjected to polishing treatment, the adopted film material and the substrate are the same material, the thermal expansion coefficient, the dielectric loss and the like are completely consistent, and the surface of the aluminum oxide HTCC thick film mixed substrate is effectively repaired. The problem of radio frequency loss of the aluminum oxide thick film mixed substrate is solved, and meanwhile, the problems of thermal mismatch and the like caused by adopting different materials are avoided. According to the invention, the surface state of the substrate is improved, the surface roughness is reduced, the subsequent thin film wiring process requirements are met, and the method can be applied to processing and manufacturing of thick thin film hybrid circuit substrates and thin film multilayer hybrid substrates for various microwave components and packaging modules.

Description

Technical Field

[0001] The invention belongs to the field of microelectronics, and in particular relates to a method for eliminating surface defects of an aluminum oxide HTCC thick film hybrid substrate. Background Art

[0002] Thick-film hybrid substrate is a new type of high-density packaging substrate that combines the advantages of traditional co-fired ceramic substrate technology and thin-film substrate technology. It can simultaneously have the characteristics of multi-layer circuit structure, high-precision surface wiring, and high heat dissipation capacity. It has broad application prospects in various types of highly integrated, high-power, lightweight, and multi-functional electronic products.

[0003] From a processing perspective, thick-thin-film hybrid substrates are manufactured by thinning and polishing high-temperature co-fired ceramic (HTCC) substrates to improve surface flatness and roughness. Thin-film processes are then applied to the substrate surface to form the final circuit wiring. Among various HTCC substrate types, alumina HTCC substrates offer excellent electrical properties, thermal conductivity, and mechanical strength, along with a high level of process maturity and low cost, making them a promising thick-thin-film hybrid substrate material.

[0004] Although alumina HTCC substrates have great advantages, there are still key issues that need to be urgently addressed during engineering applications. The alumina HTCC substrate material itself has a large particle size, and pores will be formed during processes such as sintering and debinding, eventually forming pores in the form of a volume distribution inside the substrate. Although planarization can improve microscopic conditions such as surface roughness, there will still be varying degrees of depression (diameter 5-20um, depth 4-8um), and the surface roughness is greater than 120nm, which cannot meet the requirements of high-density thin-film wiring processes. In particular, for thin-film wiring line widths below 20um, the substrate's on-off and RF performance are seriously affected. It should be noted that this type of pore depression is a volume distribution state, and further thinning and polishing methods cannot completely eliminate the defects. Therefore, the pore depression problem is a bottleneck problem that restricts the implementation and application of alumina HTCC thick-film hybrid substrate processes.

[0005] In existing technologies, the surface flatness is improved by grinding and polishing the substrate surface, and a minimum thin film line width of 20um can be achieved. However, this is close to the size of defects on the substrate surface, and the RF performance and process reliability are restricted, making it impossible to further reduce the line width. Alternatively, the surface roughness and flatness of the substrate are solved by laminating an organic film on the substrate surface, further improving the wiring density and accuracy. However, due to the use of heterogeneous materials for surface treatment, although the thin film wiring density is improved, there are reliability risks such as thermal mismatch in high-temperature application scenarios. Summary of the Invention

[0006] To this end, this paper proposes a method for effectively repairing inherent surface depressions in aluminum oxide HTCC thick-thin-film hybrid substrates. This method improves the substrate's surface condition and reduces surface roughness, meeting the requirements of subsequent thin-film wiring processes. This method can be applied to the processing and manufacturing of various microwave components, thick-thin hybrid circuit substrates for packaging modules, and thin-film multilayer hybrid substrates. Specifically, it includes the following steps:

[0007] 10) Alumina HTCC Substrate Preparation: First, sinter the alumina HTCC substrate according to the design requirements, including substrate dimensions, thickness, and number of layers. Note that unlike traditional lamination manufacturing, one or two layers of alumina raw tape are required to serve as a sacrificial layer for the chemical mechanical polishing (CMP) process on the substrate surface to compensate for substrate thickness variations caused by the CMP process. Furthermore, proper lamination and sintering parameters must be adjusted to ensure substrate flatness and a contamination-free surface.

[0008] 20) Substrate Thinning and Polishing: Sintered alumina HTCC substrates undergo a preliminary thinning and polishing process to improve substrate flatness and reduce surface roughness to meet the requirements of subsequent thin-film alumina deposition. The thickness of the thinning and polishing process must be controlled to meet design requirements. After cleaning, the substrates are measured to achieve a flatness of ≤10µm and a roughness of ≤200nm.

[0009] 30) Aluminum Oxide Film Deposition: Aluminum oxide film is deposited on the polished substrate surface using magnetron sputtering equipment. The thickness must be greater than the deepest surface depression of the substrate, generally 10-15 μm, to ensure that the substrate surface depression is completely filled. After deposition, the adhesion of the aluminum oxide film is assessed. The adhesion between the deposited aluminum oxide film and the HTCC substrate surface must pass a 3M tape pull test. The thickness uniformity of the deposited aluminum oxide film must be ≤ ±3%, and the surface must be free of particles and defects.

[0010] 40) High-precision polishing of substrate surface: The aluminum oxide substrate with the aluminum oxide film deposited is subjected to high-precision polishing again. In this step, the polishing thickness accuracy must be strictly controlled to make it less than the thickness of the deposited aluminum oxide film and greater than the maximum depth of the substrate surface depression, see Figure 6 The dotted lines are highlighted to remove excess film material while maintaining surface flatness. This step completely repairs the substrate surface depressions, with a roughness of less than 80nm.

[0011] Finally, through typical thin film process flows such as cleaning, sputtering, photolithography, electroplating, and corrosion, the manufacturing of alumina HTCC thick-film hybrid substrate based on surface defect improvement is completed.

[0012] The beneficial effects of the present invention are

[0013] 1. Low cost: The substrate process steps in the present invention are simple. Thin film deposition is performed on the surface of the alumina HTCC substrate and then polishing is performed. No new materials need to be introduced, so the cost is low and the product consistency is high.

[0014] 2. High reliability: The film material used in the present invention is the same as the substrate, and the thermal expansion coefficient, dielectric loss, etc. are completely consistent. The surface state of the substrate is comparable to the ceramic substrate used for the thin film, which solves the RF loss problem of the thick aluminum oxide film hybrid substrate and avoids the thermal mismatch problem caused by using different materials.

[0015] 3. High scalability: The process method provided by the present invention has simple process steps and can be extended to other mixed-film mixed substrate applications, for example, the preparation of thick-film mixed substrates based on thin-film multilayer technology.

[0016] 4. It has high application value and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the pore structure generated after sintering of alumina HTCC ceramic substrate.

[0018] Figure 2 This is a schematic diagram of the defect structure generated on the surface of the alumina HTCC ceramic substrate after thinning and polishing due to the bulk distribution of pores.

[0019] Figure 3 The process flow chart of the surface defect improvement method based on alumina HTCC thick film hybrid substrate.

[0020] Figure 4 Schematic diagram of the structure prepared by sintering an alumina HTCC substrate including a sacrificial layer.

[0021] Figure 5 This is a schematic diagram of the structure of defects generated on the surface of an alumina HTCC ceramic substrate after thinning and polishing.

[0022] Figure 6 Schematic diagram of the substrate structure after depositing aluminum oxide film to fill the depressions on the substrate surface.

[0023] Figure 7 This is a schematic diagram of the substrate structure after the substrate with the aluminum oxide film deposited thereon is polished again.

[0024] The meanings of the reference numerals are as follows: 1-alumina HTCC substrate sacrificial layer; 2-alumina HTCC substrate; 3-pores in the substrate; 4-depression on the substrate surface after grinding and polishing; 5-sputtered alumina film. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] like Figure 3 As shown, the present invention proposes a method for eliminating surface defects of an aluminum oxide HTCC thick film hybrid substrate, comprising the following steps:

[0027] 10) Preparation of Alumina HTCC Substrate: First, the multi-layer alumina HTCC substrate is sintered and manufactured according to the design requirements of the substrate's external dimensions, thickness, number of conductor layers, aperture, etc. Taking a 1.5mm thick alumina substrate as an example, the thickness of a single layer of raw tape is 0.1mm, and there are 17 layers of raw tape in total, of which 2 layers are used as sacrificial layers for the chemical mechanical polishing (CMP) process on the substrate surface. After sintering, the flatness of the substrate itself is ≤50um, and the surface is free of pollution. Figure 4 shown.

[0028] 20) Substrate thinning and polishing: The sintered alumina HTCC substrate is thinned and polished to further improve the flatness of the substrate and reduce the surface roughness of the substrate to meet the requirements of the subsequent thin film deposition of alumina. This step is carried out through the CMP process, using a combination of coarse grinding and fine grinding to control the thinning thickness to 1.5mm, meeting the design requirements. After cleaning, the substrate is measured and the flatness is ≤10um and the roughness is ≤200nm. Figure 5 shown.

[0029] 30) Aluminum Oxide Film Deposition: Measurements show that the depth of surface depressions on the polished substrate ranges from 2 to 8 μm. A 15 μm thick aluminum oxide film is deposited using magnetron sputtering equipment to ensure that these depressions are completely filled. After deposition, the film is tensile tested using 3M tape to verify adhesion. The thickness uniformity of the deposited aluminum oxide film is ≤ ±3%, and the surface is free of particles and defects.

[0030] 40) Substrate surface polishing: The substrate with the aluminum oxide film deposited is polished again with high precision. In this step, the polishing thickness accuracy is strictly controlled to be less than 15um of the thickness of the deposited aluminum oxide film and greater than the maximum depth of the substrate surface depression of 8um. Figure 6 The dotted part of the bright bar is removed. The excess film material is removed while ensuring the surface flatness and roughness. Through this step, the substrate surface depression is completely repaired, and the roughness is measured to be less than 80nm. Figure 7 shown.

[0031] Finally, through typical thin film process flows such as cleaning, sputtering, photolithography, and electroplating, the manufacturing of alumina HTCC thick-film hybrid substrate based on surface defect improvement is completed.

[0032] The present invention is not limited to the above specific embodiments, and various modifications and variations are possible. Any modification, equivalent replacement, improvement, etc. made to the above embodiments based on the technical essence of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for eliminating surface defects of an aluminum oxide HTCC thick film hybrid substrate, characterized by: The specific steps include: 10) Alumina HTCC Substrate Preparation: Sintering of alumina HTCC substrates is performed based on the substrate dimensions, thickness, and number of substrate layers. Alumina raw tape is added as a sacrificial layer for the chemical mechanical polishing process on the substrate surface to compensate for substrate thickness deviations. This ensures the substrate's flatness and surface contamination. 20) Substrate thinning and polishing: The sintered alumina HTCC substrate is subjected to preliminary thinning and polishing treatment, which can improve the flatness of the substrate and reduce the surface roughness of the substrate; 30) Aluminum oxide film deposition: Aluminum oxide film is deposited on the polished substrate surface by magnetron sputtering equipment. The thickness must be greater than the deepest depression on the substrate surface to ensure that the depression on the substrate surface is completely filled. 40) High-precision polishing of the substrate surface: The aluminum oxide substrate with the aluminum oxide film deposited thereon is subjected to high-precision polishing again. The thickness of the aluminum oxide film after polishing must be controlled to be greater than the maximum depth of the depression on the substrate surface to remove excess film material and ensure surface flatness; Finally, through the processes of cleaning, sputtering, photolithography, electroplating and corrosion, the manufacturing of alumina HTCC thick-film hybrid substrate based on surface defect improvement is completed.

2. The method for eliminating surface defects of an aluminum oxide HTCC thick film hybrid substrate according to claim 1, characterized in that: The step 20) further includes measuring the substrate after polishing, requiring the flatness to be ≤10 μm and the roughness to be ≤200 nm.

3. The method for eliminating surface defects of an aluminum oxide HTCC thick film hybrid substrate according to claim 1, characterized in that: The thickness of the aluminum oxide film deposited in step 30) is 10-15 μm.

4. The method for eliminating surface defects of an aluminum oxide HTCC thick film hybrid substrate according to claim 3, characterized in that: The step 30) further includes: after the aluminum oxide film is deposited, an adhesion test is required, and the thickness uniformity of the deposited aluminum oxide film is required to be ≤±3%, and the surface is free of particles and defects.

5. The method for eliminating surface defects of an aluminum oxide HTCC thick film hybrid substrate according to claim 1, characterized in that: After high-precision polishing of the substrate surface in step 40), the roughness is ensured to be less than 80 nm.

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