Chip Fabrication – Roughness Polishing Of Wafer Surfaces

 

Rough polishing of the surface of the silicon wafer

1.1 Wax-free patch single-sided polishing

As a key process to achieve high-cleanliness surfaces in semiconductor manufacturing, the core of wax-free patch single-sided polishing on silicon wafer surfaces is to achieve close bonding between silicon wafers and carrier plates through vacuum adsorption or water surface tension, avoiding organic wax contamination and simplifying the subsequent cleaning process. This process is widely used in the surface processing of silicon wafers with a diameter of < 125mm, while for 150-200mm silicon wafers, a three-step/four-step polishing strategy combining waxed and wax-free wafers is often used in the 0.5μm-0.18μm line-width IC process to balance processing accuracy and contamination control requirements. For 300mm large-diameter silicon wafers, double-sided polishing is mostly used to improve efficiency in the rough and fine polishing stages, while fine polishing and final polishing return to wax-free single-sided technology to ensure the ultimate optimization of surface nanomorphology through vacuum adsorption.

The key to the wax-free patch process lies in the selection and combination of wax-free liners and soft liners.

The IPTA wax-free liner and INSERT soft liner launched by Rodel have become the mainstream choice in the industry due to their excellent surface tension control ability - the water molecular layer on the surface of the liner in the wet state forms stable adsorption through van der Waals force to ensure that the position of the silicon wafer remains stable during the high-speed polishing process. However, the process has inherent challenges in the control of total thickness deviation (TTV) and local flatness (STIR/SFQR), and it is necessary to achieve the accuracy goals of TTV≤3-2μm and STIR/SFQR≤4-2μm through process optimization such as dynamic pressure compensation and adaptive adsorption system.

In recent years, wax-free patch technology is making breakthroughs in the direction of intelligence and environmental protection. For example, the liner with integrated nanocoating technology significantly improves the adsorption and anti-slip ability by optimizing the surface energy distribution. The machine vision-based automatic alignment system can monitor the position deviation of silicon wafers in real time, dynamically adjust the adsorption pressure distribution, and improve the TTV control accuracy to the sub-micron level. In terms of environmental protection, the application of degradable polymer liners and low-VOC cleaning agents effectively reduces environmental pollution in the production process. In addition, in response to the processing needs of ultra-thin silicon wafers, the flexible vacuum adsorption platform realizes adaptive clamping of silicon wafers of different thicknesses through pressure zone control technology, further expanding the application scope of wax-free patch process.

1.2 Wax patch polishing

As a key process to achieve ultra-precision machining, the silicon wafer and the carrier plate are firmly pasted through the wax film medium, and its accuracy control depends on the fine control of the wax coating process and the strict guarantee of the clean environment. This process often adopts liquid wax, water-soluble wax and other forms, and needs to complete the process of wax application, centrifugation, spraying and other processes in at least a level 100 clean room to ensure that the wax film thickness is about 1.5μm and the uniformity deviation is controlled within ±5%.

The HF-3511 liquid wax of NIKKA SEIKO Company in Japan is combined with the segmented variable speed wax throwing technology, which spreads the wax evenly through the initial low-speed rotation of 1000-1500r/min, and then accelerates to 3000r/min to achieve wax film flattening and avoid concave defects≤.

The surface accuracy control of the carrier plate and the ceramic disc is also critical, and it is necessary to ensure that its flatness is ≤ 0.1 μm through precision grinding and chemical cleaning, and the efficient waxing is achieved with PT-CLEANER series cleaning solution. For example, PTC#7 (pH=10.6) is used for cleaning the wax film on the surface of silicon wafers, while PTC#7S (pH=12.2) is used to achieve residue-free cleaning of residual wax on ceramic plates through alkaline hydrolysis.

The combination of the Japanese Enya MT-811B-S placement machine and the Speed Fam 59SPAW polishing machine can achieve high-precision control of 200mm silicon wafers at 18-20μm processing volume, and the indicators of STIR≤0.30μm, SFQR≤0.13μm, and GBIR≤0.80μm have reached sub-micron accuracy.

In recent years, technological breakthroughs in this field have focused on intelligence and environmental protection. The automatic wax coating system based on machine vision can monitor the thickness and uniformity of the wax film in real time, realize closed-loop control by dynamically adjusting the rotation speed and wax supply volume, and improve the TTV control accuracy to ≤1.2μm. The development of environmentally friendly water-soluble waxes reduces the cost of waste liquid treatment and the environmental burden by reducing the amount of organic solvents used. In addition, the application of degradable wax film and low-temperature waxing technology further improves process safety and sustainability.

Together, these innovations drive the development of waxed patch polishing technology towards higher precision, lower damage, and more environmentally friendly conditions, continuing to meet the stringent requirements of advanced semiconductor manufacturing for surface quality control.In recent years, technological breakthroughs in this field have focused on intelligence and environmental protection. The automatic wax coating system based on machine vision can monitor the thickness and uniformity of the wax film in real time, realize closed-loop control by dynamically adjusting the rotation speed and wax supply volume, and improve the TTV control accuracy to ≤1.2μm. The development of environmentally friendly water-soluble waxes reduces the cost of waste liquid treatment and the environmental burden by reducing the amount of organic solvents used. In addition, the application of degradable wax film and low-temperature waxing technology further improves process safety and sustainability.