What is the problem with wafer chipping? How to solve it?

Wafer cutting is a key process in chip manufacturing, which is directly related to the quality and performance of chips. In the actual production process, the chipping problem in wafer cutting occurs frequently, especially the front edge chipping and the back edge chipping, which has become a key factor restricting production efficiency and product yield. Edge chipping not only affects the appearance of the chip, but may also cause irreversible damage to its electrical properties and mechanical strength.

Definition and types of collapsed edges

Chipping refers to the cracks or breakage that occur on the edge of the chip during the wafer cutting process, which is mainly divided into front edge chipping and back edge chipping.

Frontal chipping refers to cracks or damage in some areas on the front edge of the chip with circuit graphics, and if the chipping invades the inside of the chip circuit graphics, the electrical performance and reliability of the chip will be adversely affected. The chipping on the back side mostly occurs after the thinning process, and the grinding layer is broken. From the perspective of manifestation, the front edge chipping is mostly reflected in the chip epitaxial layer cracking, while the back edge chipping is caused by the damage layer formed during the removal of the matrix material after thinning.

 

Frontal chipping can be subdivided into three types: initial chipping, cyclic chipping, and other chipping. The initial chipping usually occurs in the pre-cutting stage of new blade installation, which is manifested by irregular chipping on the wafer surface. cyclic chipping is manifested as periodic and repeated chipping on the wafer surface during the cutting process; Other chipping includes abnormal chipping due to blade deflection, improper feed speed and cutting depth, workpiece displacement deformation, etc.

Causes of edge collapse

The main reasons for initial edge chipping include insufficient blade mounting accuracy, the blade not being perfectly rounded, and the diamond not being fully exposed. The presence of tilt during blade installation will cause uneven force during cutting; If the new blade is not fully trimmed, the concentricity is not good, and the cutting trajectory is offset; If the diamond particles are not fully exposed during the pre-cutting stage, they will not be able to form effective cutting grooves, which can easily cause edge chipping.

Cyclic edge chipping is mostly caused by the impact of the blade surface, diamond bulge on the blade surface or the adhesion of foreign impurities. During the cutting process, the blade may be impacted by the flying material of the product to form a small gap; The diamond particles on the surface of the blade are unevenly distributed, and the presence of large particle bulges will cause local stress concentration. Foreign objects such as residual glue and metal adhering to the blade surface can also affect the cutting quality.

Other chipping edges are often related to blade deflection, improper feed speed and cutting depth, and workpiece displacement deformation. Insufficient accuracy of blade dynamic balance at high speed will lead to yaw; Unreasonable feed speed and cutting depth will increase the blade load; Displacement or deformation of the workpiece during cutting can cause the cutting trajectory to deviate from the preset path.

The main causes of backside chipping include thinning stress and thin wafer warping. During the wafer thinning process, a damage layer will form on the back side, breaking the lattice arrangement and generating internal stress. The stress release during dicing causes tiny cracks that fuse into a backside crack. When the wafer thickness is thinned to a certain extent, its ability to resist stress is weakened, external warping occurs, internal stress increases, and it is more likely to cause backside chipping during dicing.

The impact of edge collapse on chips and their response

The impact of edge chipping on the mechanical strength of the chip should not be underestimated. Once there are subtle cracks on the edge of the chip, these cracks may continue to expand during subsequent packaging or actual use, eventually leading to chip breakage. A chip breakage can cause electrical failure, making it impossible to function properly. If the front edge chipping invades the inside of the circuit pattern, it will directly affect the reliability and electrical performance of the chip.

For the problem of chipped edges, it can be optimized from many aspects. In terms of cutting process parameters, the cutting speed, feed rate, and cutting depth should be dynamically adjusted according to different areas of the wafer, material thickness, and cutting progress to minimize stress concentration. Machine vision and artificial intelligence technology are used to monitor the blade status and chipping in real time, and automatically adjust parameters for precise control.

Equipment maintenance is equally critical. Regular maintenance of cutting equipment ensures that the spindle accuracy, transmission system, cooling system, etc. are in good condition, reducing the risk of chipping due to equipment aging. Establish a blade service life monitoring mechanism to replace severely worn blades in time to avoid edge chipping caused by performance degradation.

In terms of tool selection, the diamond particle size, hardness of the bonded material and particle density of the dicing tool are closely related to chipping. Larger diamond particles are prone to frontal chipping, while smaller particles reduce chipping but reduce the slicing efficiency. Low density particles reduce frontal chipping while shortening tool life. Soft bonding materials reduce chipping but also reduce tool life. Therefore, it is necessary to find a balance between controlling the chipping size and production costs. For silicon-based chips, diamond particle size is the main influencing factor, and the use of high-quality dicing knife with the lowest proportion of large particles and precise control of particle size and grading can effectively deal with frontal edge chipping.

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For backside chipping, optimization measures include controlling the speed of the grinding wheel, selecting the appropriate emery, ensuring that the tool is installed correctly, and implementing post-processing. Too slow or too fast will increase the risk of chipping on the backside, and the appropriate speed should be selected according to the actual situation. The use of fine emery particle size, soft binder and low concentration of emery can reduce the chipping angle on the back. Tilting of the blade mount or vibration of the spindle can cause large areas of back chipping, so it is important to ensure accurate installation and equipment stability. For thin wafers, post-processing methods such as chemical mechanical polishing, dry etching, and chemical wet etching can remove residual defects and release stress, reduce warpage, and improve chip strength.

The introduction of advanced cutting techniques such as laser cutting and waterjet cutting is also a direction to reduce chipping. Laser cutting uses high energy density and non-contact characteristics to reduce chipping caused by physical contact. Waterjet cutting uses a high-pressure stream of water to carry tiny abrasive particles for cutting, reducing thermal and mechanical stress.

Strengthening quality control is just as important as testing. Establish a strict quality control system, from raw material procurement to finished product testing, to ensure that each process meets standards. High-precision inspection equipment such as scanning electron microscope, optical microscope, etc. is introduced to carefully inspect the wafer after cutting, and timely detect and deal with chipping defects.

The chipping problem in wafer cutting involves many factors and needs to be effectively addressed through comprehensive optimization of process parameters, equipment maintenance, tool selection, and quality control measures to improve the yield and reliability of chip production.