What is the cutting of silicon wafer?
The processing of silicon wafers is to process silicon ingots with a certain diameter, thickness, crystal orientation and height, surface parallelism, flatness, and roughness, the surface of which has undergone shaping, orientation, cutting, grinding, etching, polishing, cleaning and other processes. A highly complete, uniform and smooth mirrored silicon wafer with no defects, no chipping, no damage layer on the surface. Only by cutting the silicon chain into silicon wafers in accordance with the technical requirements can it be used as the base material for the production of solar cells. Therefore, the cutting of silicon wafer, that is, slicing, is an important step in the processing of the entire silicon wafer. The so-called slicing is to use a high-speed rotating blade (inlaid with emery abrasive) to cut the silicon ingot into slices of silicon wafers. In order to ensure the quality and yield of the slicing, the following requirements are imposed on the slicing process technology.
①The section is complete, without wire drawing, knife marks and micro cracks.
②The cutting seam should be small, and the loss of raw materials should be less.
③High cutting precision, high surface parallelism, small warpage and thickness tolerance.
④The cutting speed is fast, realizing automatic cutting.
The slicing methods currently mainly include outer circle cutting, inner circle cutting, multi-line cutting and laser cutting. Slicing generally uses an internal cutting machine to cut the silicon ingot into slices of 0.3 to 0.4 mm. In the cutting process, there is a thickness loss of 0.3~0.35mm for every slice cut. Therefore, the utilization rate of silicon material is only 40%~50%. The thickness of the inner circle cutting blade is about 0.1mm, and the thickness of the blade is 0.20~0.25mm, there is emery powder sticking to the blade. In the cutting method of the inner circle cutting machine, if the blade is installed horizontally, the silicon material is fed in the horizontal direction for cutting; if the blade is installed vertically, the silicon material is fed in the vertical direction for cutting.
Slicing with a multi-wire cutting machine is currently the most advanced slicing method. It uses steel wire to carry abrasive particles to complete the cutting work. That is, the steel wire coil is placed on the fixed frame, and the silicon wafer is cut through the rolling silicon carbide abrasive. The advantages of this method are high quality of slices, fast cutting speed, large output, low cost, low material loss (only 0.2~0.22mm), and high yield. In addition, it can be cut into larger and thinner (0.2mm) slices, which is conducive to large-scale automated production. The Swiss multi-wire cutting machine can cut 4 groups of silicon ingots at the same time. It only takes about 3.15h to cut into 4160 slices at the same time. The average thickness of each wafer is 325 pm, and the cutting edge is narrow, which can save about 1/4 of the silicon material compared with the general internal circular cutting machine.
The processing quality requirements for silicon wafers in production are very strict: when cutting silicon wafers, first ensure the crystal orientation of silicon crystals, especially single crystal silicon. In addition, there are strict requirements on the shape and position tolerance of the wafer. The diameter, thickness, height, surface parallelism, flatness, and roughness must meet the technical requirements on the drawings, and there must be no chipping, damage and other defects.