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      How are semiconductor wafers made?

      wafer is a thin piece of silicon about a millimeter thick that has a very high degree of flatness on the surface due to the very high requirements of the manufacturing process. The specific application of a wafer determines the type of wafer length required. For example, after polysilicon melts, the pencil-sized seed crystals dip into the molten silicon, then slowly rotate the seed crystals and slowly pull them upward. So you pull out a very heavy monocrystalline silicon ingot. In addition, wafers can be made to achieve targeted electrical properties by adding trace amounts of highly purified dopants to molten silicon. The silicon ingot is doped according to the customer’s specifications and then sliced and polished. After a number of processes, customers receive specially packaged wafers that meet their specific specifications and can be used instantly on their production line.

      CZOCHRALSKI PROCESS

       

       

      Most of the current monocrystalline silicon is crystallized by the direct pull method, in which the highly purified polysilicon is melted in an ultrapure quartz crucible and dopants (usually boron, phosphorus, arsenic, antimony) are added to it. A single seed crystal is dipped into the molten silicon and then slowly rotated up to gradually pull out a columnar silicon ingot with a head and tail cone. Such a head cone and tail cone can prevent dislocation caused by thermal shock.

      The temperature and flow rate of molten silicon, the speed of crystal and crucible rotation, as well as the precise control of drawing speed play a key role in obtaining high quality monocrystalline silicon ingot.

       

      FLOAT ZONE METHOD

      The zone fusion method is an ideal long crystal method for the demand of power devices such as IGBT.

      As shown, the columnar polysilicon ingot is placed above the induction coil, which is heated by a wireless magnetic field and fuses the ingot from the lower part of the polysilicon rod above the coil. The strength of the electromagnetic field can be adjusted to form monocrystalline silicon by the flow of molten silicon through the holes in the middle of the induction coil. For zone fusion, doping is usually boron or phosphorus, and is achieved by doping its gaseous substance.

       

      CYLINDRICAL GRINDING


      After cutting head cone, tail cone and post-cut quality inspection, the silicon ingot is directly drawn or fused to carry out wafer processing stage.

      These processes involve the precise alignment of the crystal segments and the grinding of the crystal cylinders of the segment to achieve the desired diameter. The last step is to add directional marking. For large-sized wafers, a cylinder surface is generally ground out a Notch as the positioning groove, while for small-sized wafers, the Flat edge is generally ground out as the positioning edge.

       

      WIRE SLICING

      The first step of silicon segment lamination is to adopt the line cutting technology, which is the mainstream slicing method at present.

      A long, thin Wire (which can be several miles long) guides the Wire Web through the Wire Guide Rollers to make a very well-spaced distribution. When the wire mesh is slowly drawn on the silicon, the cutting Nozzle injection of the Nozzle goes to the Nozzle. In this way, a single silicon section can be sliced into hundreds of silicon wafers in one process. In this process, the process parameters of each link need to be closely monitored to ensure that the wafer has a relatively uniform thickness and the silicon wafer remains relatively parallel on both sides.

       

      EDGE ROUNDING

      Monocrystalline silicon is very fragile and has a high risk of fragmentation. Therefore, special care should be taken during chamfering to avoid mechanical damage to the edge of the wafer.

      The unchamfered silicon wafer is placed on the grinding chuck, and the edge of the wafer is ground by the chamfering wheel with rounded grooves. The edge of the wafer meshes with grooves and is chamfered several times by grinding wheels with different abrasive particles, so as to produce rounded edges that meet the customer’s requirements. Chamfer is divided into T – chamfer (large chamfer) and R – chamfer (small chamfer).

       

      LASER MARKING

      A laser tag on a wafer is used to trace a single or batch of wafers in production. Laser identification can be marked according to industry standards or customer requirements. The logo usually contains information such as the wafer manufacturer’s code, some technical parameters, and the wafer number. The laser identifier above contains wafer number, manufacturer code, resistivity, dopant, orientation, calibration code, etc.

       

      LAPPING

      After the wire cutting and chamfering, the surface of the silicon wafer needs to be ground, which can improve the parallelism of the silicon wafer surface and eliminate the surface damage caused by the wire cutting process.

      During grinding, the silicon wafer is fixed on the Lapping Carrier between the upper and lower Lapping plates as shown in the figure above. When the upper and lower Lapping plates rotate in relative direction, the two sides of the silicon wafer can be ground simultaneously. Lapping enthalpy is added during the grinding process, approximately 10 microns of silicon is removed from each side of the grinding process.

       

      CLEANING AND ETCHING

      After mechanical treatment, the silicon wafer needs to be cleaned and etched to eliminate residual mechanical damage on the surface. Alkaline or acidic solutions, or a combination of both, may be used in etching treatments. The pictures above are respectively Cleaning Bath, Etch Bath and Dryer.

       

      POLISHING


      The polishing process is used to grind the silicon surface to a glossy, mirror-like state and to further improve the Flatness of the silicon wafer. During Polishing, the silicon wafers are placed on a support Plate and polished Cloth is pressed onto Polishing Plate.

      Wafers with diameters of 200mm(8 inches) or less are usually buffed on one side. Wafers with diameters of 300mm or more are usually buffed on two sides, but this is not an absolute process and depends more on customer requirements.

      Similar to the grinding process described above, the wafer is fixed between the upper and lower disks, and the upper and lower buffing disks polish the front and back of the wafer simultaneously. The amount of polishing fluid and polishing pressure determines the quality and flatness of the final finish.

       

      CLEANING

      After polishing, the wafer is physically and chemically cleaned with ultrapure water and chemicals, respectively.

       

      INSPECTION

      Wafer flatness and granularity are the key influencing factors of integrated circuit devices. Therefore, the Flatness and Particle size of each wafer must be checked by a specially designed instrument to ensure the wafer’s quality.

       

      PACKAGING

      The wafer that is inspected is then packed into a super-clean shipping Cassette and vacuum-sealed with a special moisture-proof bag. Typically, a boat contains 25 wafers; This is why the minimum order unit for wafer makers is 25 MOQ.

       

      HOUSING & SHIPPING

      The wafers are packed in shock-proof and shock-proof boxes to avoid damage to the wafers caused by shocks.