Although the processing of silicon carbide substrate is difficult, in order to make the application of single crystal silicon carbide in electronic components become the future direction of development, so that silicon carbide devices are large-scale application and promotion, it is necessary to find a way to solve the problem of difficult silicon carbide processing.

 

 

At present, the SiC material processing technology mainly has the following processes: directional cutting, chip rough grinding, fine grinding, mechanical polishing and chemical mechanical polishing (fine polishing). Among them, chemical-mechanical polishing is the final process, and its process method selection, process route arrangement and process parameter optimization directly affect the polishing efficiency and processing cost.

 

However, due to the high hardness and chemical stability of SiC materials, the material removal rate in the traditional CMP polishing process is low. Therefore, the industry began to study the auxiliary efficiency technology supporting the flattening ultra-precision machining technology, including plasma assisted, catalyst assisted, ultraviolet assisted and electric field assisted, as follows:

 

01 Plasma assisted technology

YAMAMURA Kazuy et al. first proposed the plasma-assisted polishing (PAP) process, which is an auxiliary chemical-mechanical polishing that oxidizes surface materials to a softer oxide layer through plasma, while still removing materials by abrasive friction and wear.

 

The basic principle is: through the RF generator reaction gas (such as water vapor, O, etc.) to produce a plasma containing free groups (such as OH free groups, O free radicals), with strong oxidation capacity of free groups on the surface of the SiC material oxidation modification. A soft oxide layer is obtained, and then the oxide layer is removed by polishing with soft abrasives (such as CeO2, Al2O3, etc.), so that the surface of SiC material reaches the atomic level smooth surface. However, due to the high price of PAP process test equipment and processing costs, the promotion of PAP process processing SiC chips is also limited.

 

02 Catalyst assisted process

In the industrial field, in order to explore the high-efficiency ultra-precision machining technology of SiC crystal materials, researchers use reagents for catalytic assisted chemical-mechanical polishing. The basic mechanism of material removal is that the soft oxide layer is formed on the SiC surface under the catalysis of reagents, and the oxide layer is removed by the mechanical removal of abrasive. For a high quality surface. In the literature, Fe3O4 catalyst and H2O2 oxidizer were used to assist the enhancement of chemical mechanical polishing technology with diamond W0.5 as abrasive. After optimization, the surface roughness Ra=2.0 ~ 2.5 nm was obtained at the polishing rate of 12.0 mg/h.

 

03 UV-assisted technology

In order to improve the SiC surface flattening processing technology. Some researchers have used ultraviolet radiation to assist catalysis in chemical-mechanical polishing process. Uv photocatalytic reaction is one of the strong oxidation reactions. Its basic principle is to produce active free radicals (·OH) by photocatalytic reaction between photocatalyst and electron catcher under the action of UV light.

 

Due to the strong oxidation of OH free groups. The oxidation reaction occurs on the SiC surface layer to generate a softer SiO2 oxide layer (MOE hardness is 7), and the softened SiO2 oxide layer is easier to be removed by abrasive polishing; On the other hand, the bonding strength between the oxide layer and the surface of the wafer is lower than the internal bonding strength of the SiC wafer, which reduces the cutting force of the abrasive in the polishing process, reduces the scratch depth left on the surface of the wafer, and improves the surface processing quality.

 

04 Electric field assisted technology

In order to improve the removal rate of SiC materials, some researchers have proposed electrochemical mechanical polishing (ECMP) technology. The basic principle is: by applying direct current electric field to the polishing liquid in the traditional chemical mechanical polishing treatment, the oxidation layer is formed on the SiC polishing surface under electrochemical oxidation, and the hardness of the oxide layer is significantly reduced. Abrasive is used to remove the softened oxide layer to achieve efficient ultra-precision machining. However, it should be noted that if the anode current is weak, the machining surface quality is better, but the material removal rate does not change much; If the anode current is strong, the material removal rate is significantly increased. However, too strong anode current will lead to lower surface accuracy and porosity.

 

In short, chemical-mechanical polishing is still the most potential flattening ultra-precision machining method for SiC materials, but in order to obtain high-quality SiC wafers more efficiently, the above mentioned auxiliary processes are potential options. However, due to the lack of relevant studies, the impact on SiC materials is still lack of predictability. Therefore, if we can deeply study the influence of related auxiliary processes on chemical-mechanical polishing technology, and further reveal the processing mechanism of chemical-mechanical polishing auxiliary efficiency enhancement technology by quantitative and qualitative research means, it will be of great significance for realizing the industrialization application and promotion of SiC materials.

In the manufacturing process of SiC (silicon carbide) substrate, the cutting of SiC ingot is a crucial step. It not only directly determines the surface quality and dimensional accuracy of the substrate, but also has a decisive influence on cost control. The key parameters determined by the cutting process, such as surface roughness (Ra), total thickness deviation (TTV), warping (BOW) and bending (WARP), have a profound impact on the final quality, yield and production cost of the substrate. In addition, the quality of cutting is also directly related to the efficiency and cost of subsequent grinding and polishing processes. Therefore, the development and progress of SiC ingot cutting technology is of great significance to improve the level of the entire silicon carbide substrate manufacturing industry.

 

 

Diamond saw blade, circular saw blade, elimination, large Ra difference, large warpage, wide slit, slow speed, low precision, loud noise

Electric spark: wire + current, eliminated, wide slit, large surface burn layer thickness

Mortar line: copper-plated stainless steel wire + mortar, thin wafer, high yield, low loss, slow speed and low precision, pollution, low life of wire saw

Diamond wire: consolidated abrasive + diamond wire, high efficiency, narrow slit, environmental protection, deep damage layer, fast line wear, substrate warping

 

First, the status quo of SiC ingot cutting technology

With the advancement of science and technology, SiC ingot cutting technology has made remarkable progress. At present, the mainstream cutting technology mainly includes mortar wire cutting, diamond wire cutting and laser stripping technology. These technologies differ in cutting efficiency, surface quality, cost, etc., providing a variety of options for SiC substrate manufacturing.

 

Second, the main cutting technology characteristics analysis

1. Mortar wire cutting: As a traditional cutting technology, mortar wire cutting cuts SiC ingot through the line containing abrasive and mortar. Although this method is low cost and easy to apply in mass production, it is slow to cut and may leave a deep damaged layer on the substrate surface, affecting subsequent processing efficiency and substrate quality.

 

 

2. Diamond wire cutting: Diamond wire cutting technology uses diamond particles as abrasives to cut SiC ingot through high-speed rotating lines. This method not only has fast cutting speed, but also shallow surface damage layer, which helps to improve the quality and yield of substrate. Therefore, diamond wire cutting technology is gradually widely used in the field of SiC substrate manufacturing.

 

 

3. Laser stripping technology: Laser stripping technology is an emerging cutting method, which uses the thermal effect of the laser beam to separate the SiC ingot. This technology can provide very precise cuts, significantly reducing substrate damage, and thus improving the quality of the substrate. However, due to the relatively high cost at present, laser stripping technology is mainly used in high-end fields.

 

Third, the impact of cutting technology on substrate quality and subsequent processes

The choice of cutting technology not only affects the direct quality of SiC substrate, but also has an important impact on its subsequent processing. High-quality cutting technology can reduce substrate surface damage, reduce the difficulty and cost of grinding and polishing, thereby improving the efficiency and effectiveness of the entire production process. Therefore, in the manufacturing process of SiC substrate, it is very important to choose the right cutting technology.

 

In summary, the development and progress of SiC ingot cutting technology is of great significance for improving the quality, efficiency and cost control of SiC substrate. With the continuous progress of science and technology and the intensification of market competition, the future SiC ingot cutting technology will develop in the direction of more efficient, more accurate and more economical. At the same time, with the rapid development of new energy, semiconductor and other fields, the market demand for SiC substrate will continue to grow, providing a broad space and opportunities for the development of SiC ingot cutting technology.

With the continuous progress of semiconductor technology, silicon carbide (SiC), as a high-performance material, has shown great application potential in the field of power electronic devices. However, in the preparation process of silicon carbide substrate, surface quality control is particularly critical, especially after thinning, grinding and polishing and other processes to obtain ultra-smooth surface. Among them, chemical mechanical polishing (CMP), as one of the key steps, is of great significance for removing the damaged layer left by the previous process and achieving high surface levelling. However, the traditional CMP process faces the problem of low material removal rate (MRR), which directly affects the production efficiency and cost. Therefore, exploring new technologies to improve the CMP efficiency of SiC substrate has become the focus of current research.

 

 

1. Basic principles and challenges of SiC substrate CMP

The surface damage depth of the thinned or ground SiC substrate is usually 2-5μm and requires further treatment by CMP.

CMP technology is based on the "chemical + mechanical" composite principle, through the combination of oxide layer formation and mechanical removal, to achieve surface smoothing.

 

2. Low MRR is the main problem of SiC substrate CMP, and the CMP efficiency of SiC is significantly lower than that of silicon substrate.

The impact of low MRR on production efficiency and cost:

Lower MRR results in longer time consuming SiC substrate CMP steps, increasing processing time and cost.

Even if the existing CMP method can produce qualified 4H-SiC substrate, low efficiency is still the bottleneck restricting its large-scale application.

 

CMP polishing process

 

3. Technical progress to improve CMP efficiency:

To meet the low MRR challenge, the industry has developed double-sided, batch polishing technology.

These advanced technologies have significantly reduced CMP man-hours, such as the CMP polishing time for a single batch of 10 substrates from 3-5 hours to 1 hour.

Double-sided polishing technology not only improves efficiency, but also helps maintain consistency and flatness on both sides of the substrate.

 

 

In summary, the improvement of chemical-mechanical polishing efficiency of silicon carbide substrate is the key to promote its wide application. Through the development of advanced technologies such as double-sided and batch polishing, the problem of low material removal rate in the traditional CMP process is effectively solved, the processing time is significantly shortened, and the production cost is reduced. In the future, with the continuous improvement of the performance requirements for SiC materials and the continuous innovation of polishing technology, we have reason to believe that the preparation of SiC substrates will be more efficient and economical, laying a solid foundation for the further development of power electronic devices. Therefore, the continuous exploration and optimization of CMP process will be an important way to promote the wide application of SiC materials in the semiconductor field.