This article describes the fundamental concepts of wafer backgrinding. It discusses the various processes required for back grinding, including optical detection systems that can detect defects on nonpatterned wafers. Additionally, the article describes the advanced technologies needed to perform wafer grinding. Finally, the article describes the benefits of back grinding. Its advantages are not limited to increased efficiency, but also to the production of better quality silicon devices.
Optical detection systems detect defects on nonpatterned wafers
Optical detection systems can detect fine defect patterns on nonpatterned silicon wafers. This technology enables high-throughput wafer inspection with high-resolution images. The reflected laser beam carries information on position and orientation of a defect. While a scanning electron microscope is often used for detailed patterned wafer inspection, an optical detection system can detect defects on nonpatterned silicon wafers with high-resolution images.
The challenges that unpatterned wafer inspection presents are a combination of pattern density and sensitivity. Higher pattern density and sensitivity means the minimum defect size is smaller, which helps reduce the yield-killing defects. But to decide which sensitivity is necessary, engineers must first understand how defects evolve. Then they can use the best technology. A new wave of equipment is making its way to the silicon wafer industry.
A sub-100 nm inspection tool has been developed to detect the defects on nonpatterned silicon wafers. It employs similar operating principles to larger-scale defect detection. Both methods use a DUV illumination-enhanced optical system. Some of these tools are claimed to have sub-20 nm sensitivity, and advanced image analysis algorithms ensure the highest sensitivity. High precision and accuracy is required for the motion control of the wafer stage.
Optical detection systems can detect defects on patterned wafers by employing bright-field and dark-field illumination. These technologies can also be used to detect defects at smaller geometries, but are usually reserved for R&D. In order to detect defects on patterned wafers, optical detection systems must compare the images of the test die with the adjacent die. Then, a system analyzes the reflected images and produces a defect map of the wafer surface.
A recent study reveals that optical reticle inspection is more effective than patterned wafer inspection. In fact, an optical reticle inspection system can detect defects in features as small as 90 nm. This technology can also be used for wafer measurements, including all-surface wafer measurements. Its automated analysis features also help with “lean manufacturing” initiatives. This research is a prime example of the effectiveness of optical detection systems for semiconductor and nonpatterned wafers.
The latest generation 8935 optical detection system from Surfscan delivers high-resolution images of defects and enables complete DOI pareto in a single test. It features advanced imaging algorithms, including a dedicated In-Lens Detector, which helps in defect visualization across all process steps. It also supports a wide range of defect types, including fragile EUV lithography layers, high aspect ratio trench, and voltage contrast layers. Moreover, its advanced technology allows for fast defect sourcing and separation in the same process.
The C205 broadband plasma optical defect inspection system uses a tunable broadband illumination source and new design-aware technologies to enable latent reliability defect detection. It combines high sensitivity with rapid optical wafer inspection speed to deliver an optimal ROI. The system supports wafers up to 200mm in diameter and is capable of monitoring both patterned and nonpatterned wafers. This enables companies to reduce costs by reducing manufacturing time and maximizing productivity.
Advanced technologies required for wafer backgrinding
Wafer backgrinding is a critical step for semiconductor manufacturing because it is essential for the successful fabrication of silicon chips. This technique uses three detailed processes to cut and polish wafers. The first step involves the application of tape lamination to the front of the wafer. Next, the backside of the wafer is ground and a blue thin tape is inserted between the wafer and the tape. This step serves as a preparatory step for chip separation.
Backgrinding reduces the thickness of the back-ground wafer from 800-700 um to 80-70 um. The remaining thickness can be used for different processing processes, such as wet and dry etching, polymer curing, lithography, and etching. Using advanced technologies, backgrinding improves the wafer/die strength. By improving the flatness of the carrier, backgrinding also increases the TTV.
The global wafer backgrinding tape market is forecasted to reach $201.6 million in 2020 and $316.9 million by 2030. Backgrinding is a key step in the manufacturing process of semiconductors, allowing high-density packaging and stacking. Backgrinding reduces the thickness of the wafer so that it can be used for ICs. It can also reduce the thickness of the wafer, making it easier to assemble chips in high-density packaging.
Several advanced technologies are required for backgrinding. The most common process is mechanical backgrinding, which is less expensive than plasma or chemical etching. However, it is not without its drawbacks. The process of backgrinding creates mechanical stress and heat on the backside of the wafer. Additionally, the size of the grits is directly related to the pressure applied to the wafer.
As the size of handheld and portable devices decreases, so do the requirements for thinning and thickness. Despite advances in wafer thickness reduction techniques, the need for high-quality wafer backgrinding equipment has become more important than ever. During the backgrinding process, a characteristic scratch pattern is left on the wafer. Certain areas of the wafer exhibit a primarily vertical pattern of scratches.
These processes can reduce the thickness of wafers, but it can lead to more defects on the backside. Because these defects are more prominent on thinner wafers, advanced technologies are required to ensure that the final product is as good as possible. Further, the backside of the wafer is smoother than the frontside, which makes the next step more difficult. Wafer backgrinding is an essential process in semiconductor manufacturing.
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Processes that reduce wafer thickness to allow high-density IC packaging
In order to produce ultra-compact electronic devices, the IC packaging industry has turned to processes that reduce the thickness of semiconductor wafers. Today, semiconductor wafers can be less than 75 mm thick. This is done by grinding the backside of the wafer. The result is a wafer that is between 75 and 50 mm thick. High-density IC packaging is possible only when the thickness of the wafer is reduced to such a small level.
The process reduces wafer thickness so that the package can be thinner than the wafer itself. This technique is particularly useful for applications that require high functionality per volume. However, it’s not a perfect process. It requires more steps and a higher initial cost. Further, the process is also costly, as it requires a higher-than-nano-scale manufacturing facility.
Besides the reduction in thickness, it also allows for a thin system-in-package. This technique is particularly useful for fan-out packages, wet seed laminated substrates, and flexible electronics. These thin embedded die are also useful for sensors and hybrid electronics. However, the thickness of these devices is a key metric for IC packaging, and it can only be reached through a complex process.
Several different techniques can be used to reduce wafer thickness to facilitate high-density IC packaging. The DAG process, for example, thinning the wafer, uses a cutting blade to saw the wafer through completely. The blade size, thickness, and rotation speed of the saw affect the quality of the finished product. Blade chipping can be problematic, so it’s often wise to mount the wafer on a glass substrate to minimize the risk.
The main disadvantages of the process of thinning silicon is that it ruins the crystal structure of silicon. This happens due to thermal cycling. The lower the thermal cycling, the lower the bond stress, and the more the die flexes. Moreover, the inherent residual damage to silicon crystal lattice can degrade the device’s performance. If this process is not done correctly, the resulting wafer may not be able to meet the specifications.
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