CNC Knowledge: Key Points of the Platelet Thinning Process

As an important process in semiconductor manufacturing, wafer thinning is inseparable from the complex circuits and performance ensured by carefully thinned wafers. As a key technology in semiconductor manufacturing, wafer thinning is of great importance to improve chip performance, optimize package design, and improve heat dissipation efficiency. This article will provide an in-depth analysis of the key points of the wafer thinning process and provide a reference on the process.

1. Why does the blister need to be diluted?

Wafer thinning refers to the process of reducing the thickness of the original silicon wafer to a specific range through a series of precision processes. This process is invaluable for improving chip performance, optimizing package design, and improving heat dissipation efficiency. With the rapid development of semiconductor technology, the trend of chip miniaturization and integration has become more and more obvious, and wafer thinning has become one of the key technologies to achieve this goal. .

2. Main methods of platelet thinning

There are many wafer thinning methods, but the most common and mature ones mainly include mechanical grinding, chemical-mechanical polishing (CMP), wet etching and plasma dry chemical etching. Each method has unique advantages and applicable scenarios.

Mechanical grinding

Mechanical grinding is one of the first technologies applied to wafer thinning. It uses a grinding wheel containing diamond particles to cut the surface of the insert at high speed to achieve the goal of thinning.

This method has the advantages of high efficiency and low cost, but it also has the disadvantages of easy introduction of scratches and high mechanical stress.

In order to overcome these problems, modern mechanical grinding processes often adopt a multi-step grinding strategy, that is, first use a coarse-grained grinding wheel for coarse grinding to remove most of the excess material, then gradually move to fine grinding. Grain wheel for fine grinding to achieve a smoother insert surface.

Chemical Mechanical Polishing (CMP)

Mechanical-chemical grinding is a composite process that combines chemical etching and mechanical grinding. During the CMP process, the surface of the wafer is coated with a special chemical solution (polishing solution). Chemical components in the solution may react chemically with the wafer material and soften its surface.

At the same time, the polishing pad or polishing cloth exerts a certain pressure and rotation on the surface of the insert, further removing the softened material by mechanical friction. CMP technology can effectively reduce wafer surface roughness and improve flatness. This is one of the current common processes of platelet thinning.

Wet etching

Wet etching is a method that uses chemical agents to evenly etch the surface of the wafer. This method achieves precise control of wafer thickness by controlling parameters such as etchant concentration, etching temperature and time. Wet etching has the advantages of simple process and low cost, but environmental conditions must be strictly controlled during the process to avoid excessive corrosion or wafer damage caused by the etchant.

Plasma dry chemical etching

Plasma dry chemical etching is a high-tech technology that uses plasma reactions on thin wafers. In a plasma environment, gas molecules are ionized into charged particles, which react chemically with the wafer surface to remove material. Compared with wet etching, plasma dry chemical etching has higher processing precision and fewer heat-affected zones, but the equipment cost is higher and the operation is more difficult.

3. Key steps in the platelet thinning process

Regardless of the thinning method used, the course of the platelet thinning process is approximately the same, and mainly includes the following points:

Platelet preparation

Before thinning the wafer, it must first be thoroughly cleaned and inspected to remove surface impurities and defects. The cleaning process generally includes multiple cleanings using cleaning agents such as deionized water and organic solvents, and the cleaning effect is improved through ultrasonic waves, rotating sprays and other methods. The inspection mainly uses optical microscopes, scanning electron microscopes and other equipment to observe the surface of the wafer to ensure that there are no cracks, scratches and other quality problems.

protective mask

In order to prevent the wafer surface from being damaged or contaminated during the thinning process, it is usually necessary to cover the wafer surface with a layer of photoresist or other protective materials serving as a mask . This step is carried out through the photolithography process, that is, after the photoresist is evenly applied to the surface of the wafer, a specific pattern is formed through exposure, development and other steps. Mask pattern design requires precise calculation and adjustment based on circuit layout and wafer thinning requirements.

Slimming process

The slice is thinned according to the thinning method chosen. During mechanical grinding and CMP processes, it is necessary to control the rotational speed, pressure, feed and other parameters of the grinding wheel or polishing pad to ensure the uniformity and precision of the thinning of platelets. During wet etching and dry chemical plasma etching processes, it is necessary to precisely control the concentration, temperature, time and other parameters of the etchant or plasma to avoid unnecessary damage to the slice.

Cleaning and inspection

Once the thinning process is complete, the insert must be thoroughly cleaned to remove abrasive powder residue, polishing fluid, corrosives and other substances. The cleaning process also requires strict control of parameters such as cleaning agent type, concentration, temperature and cleaning duration. After cleaning is completed, the wafer should be inspected again to ensure that there are no scratches, residues or other quality issues on the wafer surface.

Antistatic treatment

Since wafers are extremely sensitive to static electricity during manufacturing and processing, which can damage circuitry or degrade performance, antistatic treatment is an indispensable part of the wafer thinning process. Once the wafer is cleaned and inspected, an anti-static coating is typically applied or the wafer is placed in an anti-static environment for further operations. Antistatic coatings can effectively neutralize electrostatic charges on the wafer surface, reduce the occurrence of electrostatic discharge (ESD) events, and protect the wafer from damage.

4. Points of attention in the process of platelet thinning

Uniformity and precision control

The uniformity and precision of wafer thinning directly affects chip performance and reliability. In order to achieve high-precision thinning, various parameters of thinning equipment, such as rotation speed, pressure, feeding speed, etc., must be strictly controlled and precisely calibrated and adjusted. In addition, the use of advanced online monitoring technologies, such as laser thickness gauges, optical interferometers, etc., can monitor wafer thickness changes in real time and adjust process parameters in time. timely to ensure uniformity and precision of thinning.

stress management

Some mechanical and thermal stresses will be generated during the wafer thinning process, and these stresses can lead to wafer deformation, cracks and other problems. To effectively manage stresses, the wafer can be pretreated before thinning, such as annealing, to remove internal stresses. At the same time, low-stress materials or optimized process parameters should be used during the thinning process to reduce stress generation and accumulation. Additionally, the thinned wafer must undergo stress relief treatment, such as re-annealing, to ensure the stability and reliability of the wafer.

damage control

During the wafer thinning process, if it is not handled properly, it is easy to cause scratches, holes and other damage to the wafer surface. In order to control damage, high-quality dilution equipment and materials should be selected, such as high-purity grinding wheels, polishing pads and polishing fluids. At the same time, process control must be strengthened, for example by optimizing grinding or polishing paths, adjusting parameters such as pressure and speed, to reduce the mechanical impact on the insert surface . Additionally, advanced cleaning and detection technology is used to quickly detect and repair potential damage issues.

cost control

The cost of wafer thinning process is relatively high, mainly due to the equipment investment, material consumption and process complexity. In order to reduce costs, this can be achieved by optimizing process flow, improving equipment utilization and reducing material consumption. For example, using multiple wafer simultaneous thinning technology can significantly improve production efficiency and reduce unit costs; By recycling and reusing liquid waste and waste generated during the thinning process, resource waste and costs can also be effectively reduced.