High-efficiency low-damage grinding fluid for monocrystalline silicon wafer and preparation method of high-efficiency low-damage grinding fluid

Abstract

The invention relates to the technical field of semiconductor grinding and polishing, in particular to a high-efficiency low-damage grinding fluid for monocrystalline silicon wafers, a main grinding material is a diamond / cerium oxide composite main grinding material prepared by performing vacuum plating on diamond micro-powder and cerium nitrate hexahydrate in a vacuum furnace, and the mass fraction ratio of the diamond micro-powder to cerium oxide is 7: 3; the additive is a nano silicon dioxide sol suspension, and the balance is pure water; the mass fraction ratio of the pure water to the main abrasive to the suspension liquid is 30: 10: 2; the cerium oxide releases Ce < 3 + > ions through a chemical-mechanical coupling effect in the grinding process, the Ce < 3 + > ions and the surface of the monocrystalline silicon wafer are subjected to an oxidation-reduction reaction, and delta Glt is generated; 0, the grinding resistance is reduced; and a Ce2O3 protective film is formed at a high temperature through a self-repairing mechanism of the cerium oxide layer, so that the damaged edges and corners of the diamond micro-powder are repaired.

Description

Technical Field

[0001] This invention relates to the field of semiconductor grinding and polishing technology, specifically to a high-efficiency, low-damage grinding slurry for single-crystal silicon wafers and its preparation method. Background Technology

[0002] In the manufacturing of 8-inch and 12-inch silicon wafers for semiconductors, the LAP (Lapping) process is primarily used for precision machining of silicon wafers. It utilizes free abrasive particles to remove minute amounts of material from the workpiece surface. Examples of such abrasive particles include... Figure 1 The grinding disc device shown has the following process characteristics: it can eliminate the surface damage layer left by previous processes such as cutting and grinding, improve geometric accuracy (such as flatness and thickness consistency), and reduce surface roughness to the micrometer level (Ra 0.1–1 μm), thus preparing for subsequent polishing and improving its surface flatness, thickness uniformity and mechanical properties.

[0003] Taking a 12-inch silicon wafer as an example, after wire cutting or internal circular sawing, mechanical stress layers and microcracks (Subsurface Damage, SSD) are left on the surface and edges. Laser Abrasive Polishing (LAP) removes surface damage (typically a few micrometers to tens of micrometers) through grinding, reducing defects in subsequent processes (such as fragmentation and microcracks). Furthermore, the thickness of the cut silicon wafer may have localized deviations (such as "wavy edges" or "thicker in the center and thinner at the edges"). LAP, through mechanical grinding with abrasives (such as alumina or diamond powder), can achieve uniform wafer thickness (tolerance controllable within ±1μm) and reduce surface roughness to 0.1~0.3μm, preparing it for chemical mechanical polishing (CMP) and providing a foundation for subsequent polishing or coating. The abrasives used primarily include alumina (Al2O3), silicon carbide (SiC), or diamond powder.

[0004] Traditional LAP (Laminated Abrasive Process) uses alumina (Al2O3) abrasive with a fixed particle size. Al2O3 is a widely used abrasive material in precision grinding, polishing, and surface treatment, and plays a crucial role in these fields. However, alumina abrasive powder has the following disadvantages: 1. High hardness but also high brittleness, the particles are easily broken and form sharp edges, which may cause scratches or subsurface cracks (SSD) on the workpiece surface, requiring additional etching repair, increasing costs; 2. Alumina particles are prone to settling, so dispersants (such as PEG and surfactants) need to be added to maintain uniformity; otherwise, the grinding effect will be affected. 3. In CMP polishing, alumina is mainly removed mechanically, with weak chemical corrosion, resulting in lower polishing efficiency than CeO2 or SiO2. 4. Semiconductor-grade high-purity alumina (>99.99%) has a complex preparation process and high cost. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-efficiency, low-damage polishing slurry for single-crystal silicon wafers and its preparation method.

[0006] The technical solution of this invention is: A high-efficiency, low-damage polishing slurry for monocrystalline silicon wafers comprises a diamond / cerium oxide composite abrasive prepared by vacuum deposition of diamond micropowder and cerium nitrate hexahydrate in a vacuum furnace. The mass fraction ratio of diamond micropowder to cerium oxide is 7:3. The additive is a nano-silica sol suspension, and the remainder is pure water. The mass fraction ratio of pure water, main abrasive, and suspension is 30:10:2. During the grinding process, cerium oxide releases Ce through a chemical-mechanical coupling effect. 3+ Ions react with the surface of the single-crystal silicon wafer in a redox reaction with ΔG<0, reducing grinding resistance; and the self-healing mechanism of the cerium oxide layer forms a Ce2O3 protective film at high temperature, repairing the damaged edges of the diamond micropowder.

[0007] A method for preparing the aforementioned grinding fluid, comprising: Diamond and cerium nitrate hexahydrate were used as raw materials and vacuum-coated in a vacuum furnace to prepare a diamond / cerium oxide composite abrasive, wherein the mass fraction of cerium oxide was 30%. Pure water, diamond / cerium oxide composite abrasive, and nano-silica sol suspension were mixed in a mass ratio of 30:10:2. After stirring evenly, the density of the grinding slurry was 1.20-1.25 g / ml.

[0008] In a further embodiment, the diamond particle size is 70, with a particle diameter of 1~5μm.

[0009] In a further proposed solution, the vacuum coating temperature is 700℃.

[0010] The beneficial effects of this invention are: by optimizing the abrasive combination, this invention achieves high-efficiency and low-damage processing of silicon wafers; compared with the existing grinding process, with the other processing parameters remaining unchanged, such as the grinding fluid flow rate, the lower platen speed, the sun gear speed, etc., the processing time is shortened by 1 / 3, all indicators can meet the qualified standards, and the silicon wafers processed by this new LAP composite abrasive formula have a crack rate and scratch rate of 0%. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of the grinding disc used in the grinding process of this invention. Detailed Implementation

[0012] To enable those skilled in the art to more clearly understand the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0013] This invention provides a high-efficiency, low-damage polishing slurry for monocrystalline silicon wafers. Its formulation consists of a main abrasive, additives, and pure water, with a mass fraction ratio of pure water, main abrasive, and suspension of 30:10:2. Main abrasive: Diamond micron powder (particle size 1~5μm, particle size 70) and cerium nitrate hexahydrate are prepared by vacuum coating process to obtain diamond / cerium oxide composite main abrasive. The mass fraction ratio of diamond to cerium oxide (CeO2) is 7:3, which improves cutting efficiency and reduces scratches. Compared with composite abrasives of other components, diamond micron powder / cerium oxide composite abrasive has the following advantages: Cerium oxide releases Ce through chemical-mechanical coupling during grinding. 3+ Ions react with the silicon wafer surface in a redox reaction (ΔG<0), reducing grinding resistance; and the self-healing mechanism of the cerium oxide layer can form a Ce2O3 protective film at high temperatures, repairing the damaged edges of the diamond micropowder. Additive: Nano silica (SiO2) sol suspension, used to fill microcracks and reduce frictional heat.

[0014] This embodiment also provides a method for preparing the above-mentioned grinding fluid, including: Preparation of main abrasive: Diamond with a particle size of 70 and a particle diameter of 1~5μm and cerium nitrate hexahydrate were used as raw materials. Vacuum coating was carried out at 700℃ using a GSL170X vacuum furnace to prepare diamond / cerium oxide composite main abrasive, wherein the mass fraction of cerium oxide was 30%. The above-mentioned grinding fluid was prepared by mixing diamond / cerium oxide composite abrasive with nano-silica sol suspension and pure water (pure water: abrasive: suspension = 30:10:2) and stirring evenly. The density value was controlled within the range of 1.20-1.25 g / ml.

[0015] Example 1: The double-sided polishing machine used in this invention is a DLM32B5W-ZJS 12-inch double-sided polishing machine. The polishing fluid consists of H2O, polishing powder, and a suspension. The polishing powder is the aforementioned diamond / cerium oxide composite abrasive, and the suspension is a nano-silica (SiO2) sol suspension. The DLM32B5W-ZJS 12-inch double-sided polishing machine is a fully automatic double-sided polishing device. The detailed fluid preparation steps are as follows: 1. Open the manual switch for the water inlet valve and visually inspect the water level line in the grinding tank. When the pure water level in the grinding tank is higher than 60L, start the "sand pump speed" and "stirring speed" functions in automatic mode. Do not turn them off until the grinding tank is completely emptied and cleaned, ensuring that the solution is constantly circulating and stirring. Otherwise, the sand pump may become clogged. Once the calculated water level line is reached, close the "manual switch for the water inlet valve". 2. Measure the specified amount of suspension into the grinding container using a measuring cup; then add the grinding powder in the following proportions (grinding solution ratio: 60L water, 4L suspension, 20kg grinding powder). 3. After the grinding tank automatically stirs for 5 minutes, take a certain amount of grinding liquid using a 250ml graduated cylinder and measure the density of the grinding liquid using a densitometer. The density value should be controlled within the range of 1.20-1.25g / ml.

[0016] After the polishing slurry was prepared, an experiment was conducted. Sixty silicon wafers were processed in a LAP mill. Compared with the existing polishing process, the processing time was reduced by 1 / 3. The other processing parameters remained unchanged, such as polishing slurry flow rate, lower platen speed, and sun gear speed. The process was the same as the conventional process. The evaluation was carried out according to the following evaluation items (as shown in Table 1). The evaluation results were all qualified. The silicon wafers processed by the new LAP composite abrasive formula had a crack rate and scratch rate of 0%.

[0017] Table 1 Evaluation Items for Experimental Pieces

[0018] In terms of capacity improvement, because the processing time is reduced by one-third, the optimized abrasive processing conditions can achieve the goal of increasing capacity and improving product quality while keeping other process conditions unchanged. Regarding cost, since the silicon wafer processing time is shortened, more silicon wafers can be processed in the same amount of time, resulting in a significant reduction in the unit consumption of polishing slurry. In summary, this solution reduces processing time and polishing slurry usage, lowers costs, improves production efficiency, and enhances product quality, thus achieving the ultimate goal of cost reduction and efficiency improvement.

[0019] The above description is merely a preferred embodiment of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-efficiency, low-damage polishing slurry for single-crystal silicon wafers, characterized in that, The main abrasive is a diamond / cerium oxide composite abrasive prepared by vacuum deposition of diamond micro powder and cerium nitrate hexahydrate, wherein the mass fraction ratio of diamond micro powder to cerium oxide is 7:3, the additive is nano-silica sol suspension, and the remainder is pure water; the mass fraction ratio of pure water, main abrasive, and suspension is 30:10:2; during the grinding process, cerium oxide releases Ce through chemical-mechanical coupling. 3+ Ions react with the surface of the single-crystal silicon wafer in a redox reaction with ΔG<0, reducing grinding resistance. Furthermore, the self-healing mechanism of the cerium oxide layer forms a Ce2O3 protective film at high temperature, repairing the damaged edges of the diamond micropowder.

2. A method for preparing the grinding fluid as described in claim 1, characterized in that, include: Diamond and cerium nitrate hexahydrate were used as raw materials and vacuum-coated in a vacuum furnace to prepare a diamond / cerium oxide composite abrasive, wherein the mass fraction of cerium oxide was 30%. Pure water, diamond / cerium oxide composite abrasive, and nano-silica sol suspension were mixed in a mass ratio of 30:10:

2. After stirring evenly, the density of the grinding slurry was 1.20-1.25 g / ml.

3. The preparation method according to claim 2, characterized in that, The diamond has a particle size of 70 and a particle diameter of 1~5μm.

4. The preparation method according to claim 2, characterized in that, The vacuum coating temperature is 700℃.

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