How to do Back Grinding and Wafer Polishing?

The back grinding technique should evolve as new defects in the wafers are discovered. It can change the order of processes, the chemical etching process or even the front-end process. This method has been modified numerous times. However, it has remained the most effective one so far. Below is a brief introduction to back grinding. This technique is also known as mechanical backgrinding. It is one of the most widely used techniques in semiconductor manufacturing.

Mechanical backgrinding

The process of backgrinding a semiconductor wafer uses a grinding wheel to apply pressure to the wafer’s back side. This pressure is controlled by the computer process control tool 140 by a continuous measurement loop. The pressure measured during backgrinding is the difference between the initial pressure on the sensors 112 and the pressure applied by the backgrinding wheel 150. There are three main pressure control points in mechanical backgrinding: the grinding wheel 150, the chuck table, and the chuck table.

The back grinding process involves three detailed steps. The first step is tape lamination, in which adhesive tape is applied to the front of the wafer. Once the tape is adhered to the wafer, the grinding process begins. The grinding force spreads the silicon compound in all directions, which can lead to cracks or damages on the wafer’s surface. The larger the wafer, the more susceptible it is to breaking. The best way to protect a wafer from damage is to tape it with thin blue ultraviolet tape.

Another step in the backgrinding process is to apply adhesive tape to the chuck table. This tape has holes drilled into its surface that are designed to apply pressure to the wafer while it is in the backgrinding process. After the backgrinding process, the wafer is moved to one or more machines for polishing, tape removal, and other steps in the processing. The process of multiple-concurrent backgrinding is a good example of multi-step grinding.

Another step is to change the order in which these processes are performed. For instance, the method used to backgrind a wafer has undergone many changes. A typical 50-mm-thick wafer requires two grindings: a fine-grained wafer is grinded, followed by super fine grinding. On the other hand, a thin wafer requires more grinding than a thick one.

The researchers used different types of tapes to protect patterned silicon wafers during the backgrinding process. They also performed grinding experiments on silicon wafers with tapes of varying thicknesses. While tapes offer good protection for patterned wafers, they also have some disadvantages, namely a reduction in PV value, surface roughness, and subsurface damage. The researchers hope that their findings will help them understand the role of tapes in backgrinding.

Mechanical polishing

Mechanical polishing of wafers involves the slurry particles of an abrasive substance being displaced in a circular or elliptical pattern on the surface of the wafer. The slurry particles generate various contaminants, such as metal ions and organic residues. To minimize these contaminants, mechanical polishing is a viable solution. In this article, we’ll look at two common methods.

Chemical mechanical polishing (CMP) is a technique used to polish a wafer’s top surface using a chemical process. In this process, abrasive grit is suspended in a chemical agent, which reacts with the abrasive material and accelerates the removal of material. Logitech Chemical Mechanical Polishing systems are highly versatile and are designed to be used for various polishing applications.

In one example, a chemical-mechanical polishing apparatus traverses a wafer while continuously applying the polishing fluid onto the cloth. This process is similar to a wet-drying method, except that the cloth is not in contact with the wafer. It uses a polishing fluid that can be supplied and used easily. A device for supplying the fluid and the polishing cloth is shown at arrow 9.

Chemical-mechanical polishing has a variety of applications in semiconductor manufacturing, including trench insulation and trench fabrication. The technique is primarily used in the fabrication of 16-megabit DRAMs. It is also used in planarization of intermetallic dielectrics. Its high-speed mechanical properties are critical for advanced process nodes, such as GaSb. In addition, the process can be performed at much lower cost than conventional polishing methods.

Chemical-mechanical polishing combines mechanical abrasion with chemical etching attack. The process can yield surfaces with a local roughness of one or two angstroms and global residual topography of a wafer in the two-nanometer range. Mechanical polishing has a relatively long time-frame and requires specialized equipment, but is increasingly popular. If your wafer is damaged, you can either repair it or remove it. However, removal is a viable option and it’s often a good way to improve your production process.

A single-pass CMP process is an ideal solution. The process can be applied to a wide range of materials and can yield both coarse and fine polishing. The MRR and RMS roughness of GaSb wafers were measured using a laser interferometer, white light interferometer, and atomic force microscope. These techniques were then used to characterize the surface morphology, crystalline quality, and strain defects.

Strain layer

High-angular-resolution electron backscatter diffraction was used to evaluate the distribution of elastic strains in grinding-induced damage layers in silicon carbide wafers. TEM revealed that the layers were divided into two types according to the distribution of lattice defects and elastic strains. In the 0.6-mm thick defective region, large elastic strains were found, and the abrasive interaction also caused lattice defects.

Surface scratches are similar to micro-cracks, but their magnitude is higher. They break the grain boundary of the material and generate more dislocations, promoting the nucleation of the micro-crack. Some surface scratches may also break the stable state of the material, accelerating the extension of the micro-crack. As the result of the grinding process, the surface of the wafer is roughened to a high degree, exposing the micro-crack.

The back side of the wafer is also ground to produce a strain layer. The gettering effect of the strain layer suppresses the motion of heavy metals in the wafer. Consequently, the dies cannot be formed to their full capacity and thereby, the strength of the devices is reduced. The process may result in a decrease in quality and life. Further, strain layer is also associated with the emergence of a crack in the wafer.

Mechanical grinding is the most common method for thinning wafers. Commercially available grinding systems perform this process in a two-step process. The first step involves coarse grinding at a rate of five um/sec and the second step removes the damage layer from the surface. X-ray topography and interference contrast microscopy have revealed that the damage layer formed during mechanical grinding occurs mainly at a depth of 20 um.

Although grinding provides the highest rate of Si removal, it produces subsurface damage, which is incompatible with subsequent processing. Regardless of the Si thickness and the type of wafer handling system, this mechanical damage can never be fully removed. CMP after grinding, however, has removed most of the damage associated with grinding. Using grinding plus CMP, Si can be thinned to a thickness of five millimeters, and a vacancy defect was detected. In addition, grinding with dry etch revealed voids, while grinding after CMP removed the grinding damage.

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Machines used to grind wafers

A multi-step grinding process can optimize productivity and eliminate the need for a separate polishing step. Wafers typically start at 720 um thick and then undergo coarse and fine grinding steps. A typical two-step backgrinding operation features dual spindles with grinding wheels mounted on each. The proposed configuration allows for easier spindle angle adjustments. A multi-step grinding process can grind wafers as large as 300 mm in diameter.

Surface grinding and polishing machines are used in the manufacturing of mono-crystalline and multi-crystalline wafers. The Surface Grinding/Polishing Machine 72/860 polishes silicon bricks to a mirror-like finish. The machine requires that the bricks be chamfered, rounded, and squared before it can be ground. A round grinding machine is then used to complete the process. A chamfering machine is also used to grind round silicon bricks.

Double-sided grinders are highly efficient and are capable of producing uniform roughness and flatness on both sides of the wafer. These machines can replace the ID cutting and lapping processes. A newer technology, wire cutting, is becoming a popular method for silicon wafer grinding, despite its lower cost compared to the previous techniques. The high precision of these machines allows them to achieve flatness data of 0.5 um or better. They are fully automated and can produce a uniform, flat surface.

Mechanical backgrinding machines are the most common method for thinning wafers. It is more cost effective than plasma etching and requires less time. However, it has the disadvantage of causing scratches on the backside of the wafer. Additionally, it produces heat and mechanical stress, which can damage the wafer’s surface. Unlike plasma etching, this process does not generate a vapor phase, which is the preferred method for manufacturing ICs.

Grinding wheels 101 are a common part of many machines. The wheels can be either coated with diamonds or a combination of these. Grinding wheels can also be used to perform coarse and fine grinding. The grinding wheels can also be tilted relative to the wafer. The tilting motion is controlled by a motor 104 or a separate control motor. If a grinding wheel is too rough, the etching process may not be effective.