How to Choose the Befitting Abrasive for CMP Polishing

With the ongoing development of integrated circuit technology, the precision of surface processing has reached new heights, particularly in semiconductor manufacturing and the optical field. The shrinking dimensions of features and the implementation of high-density devices underscore the importance of planar surfaces between integrated circuit materials. As a result, the efficiency of ultra-precision surface treatment and the quality of the finished surfaces are more critical than ever.

CMP technology stands out as the only method capable of achieving global planarization. In the optical sector, the manufacturing of window materials, such as resin lenses and various infrared glasses, also necessitates high precision and quality of surface finish. CMP plays an essential role in these precision machining processes, ensuring that materials meet the stringent requirements for both flatness and gloss.

The CMP process relies on the synergistic effects of chemical and mechanical actions between the polishing slurry and the material being polished, making the choice of polishing slurry a significant factor in CMP performance. The slurry is a mixture of ultra-fine solid abrasives and chemical additives, typically appearing as a white, uniformly dispersed paste. It serves functions such as grinding and chemical etching, with key components including abrasive particles, chemical additives, and pH-adjusting agents. The abrasives primarily engage in mechanical actions through micro-cutting and scratching during the polishing process.

According to recent data, polishing materials account for 7% of the value in semiconductor materials, with polishing slurries comprising 49% of the total cost of CMP materials. Notably, abrasives make up approximately 50% to 70% of the cost of the slurry itself, highlighting their importance in semiconductor processes as well as in the optical field.

The three most commonly used abrasives in CMP are SiO2, CeO2, and Al2O3. Selecting the appropriate abrasive for different materials during the precision CMP process involves considering several factors:

Material Hardness

The hardness of the material being processed greatly influences the choice of abrasive. For harder materials, such as sapphire and aluminum nitride, harder abrasives like aluminum oxide (Mohs hardness of 9) are preferred to enhance efficiency. Conversely, silicon dioxide, while providing superior surface finish, is often selected for softer materials.

Surface Precision Requirements

Different applications necessitate varying levels of surface precision and gloss. For instance, stainless steel, silicon wafers, and aluminum nitride ceramic substrates often require mirror-like finishes. In contrast, for sapphire materials, those requiring a high surface quality may favor silicon dioxide polishing slurries, while efficiency-driven processes opt for aluminum oxide.

Chemical Reaction Characteristics

CMP is a chemically and physically driven process, where the PH of the slurry plays a crucial role. The choice of abrasive may depend on whether an acidic or alkaline polishing slurry is employed, influencing overall performance.

Cleaning Difficulty

The ease of cleaning the equipment can also affect abrasive selection. For instance, switching between aluminum oxide and silicon dioxide requires thorough cleaning to prevent cross-contamination. Silicon dioxide abrasives are prone to crystallization, necessitating meticulous cleaning to avoid scratches on the polished surfaces.

In conclusion, as the semiconductor and optical industries continue to evolve, the importance of selecting the right CMP abrasives cannot be overstated. The interplay of material hardness, surface quality requirements, chemical compatibility, and cleaning challenges all contribute to the effectiveness of the CMP process, ensuring that manufacturers can meet the stringent demands of modern technology.