Chamfer is to grind away the sharp edges and corners around the wafer. Its purpose is to make the mechanical strength of the wafer bigger prevent the wafer edge from cracking, to prevent damage caused by thermal stress, and to increase the flatness of the epitaxial layer and the photoresist at the wafer edge. Generally, one side of the edge surface after processing is circular (R-type) or T-shaped (T-type). PAM-XIAMEN can offer wafers with chamfer in edge, more information please consult us.
The specific process is that the wafer to be processed is fixed on a support that can rotate at high speed, and there is a high-speed rotating diamond chamfering grinding wheel in the direction of the edge. To achieve the required diameter dimensional tolerance and edge contour shape, the edge surface grinding process of the silicon wafer is completed. Chamfer processing is shown as figure 1:
Fig. 1 Schematic Diagram of Chamfer Processing
1. Why Semiconductor Wafer Needs Chamfer?
After cutting, the surface of the wafer has edges and corners, burrs, chipping, and even small cracks or other defects, and the surface of the edge is relatively rough. In order to increase the mechanical strength of the edge surface of the slice and reduce particle contamination, the edge surface should be ground into a round or other shape. At the same time, it can also avoid and reduce the collapse of the following processes during processing, transportation, inspection and other processes. Since the chamfered wafer has a relatively smooth edge, it is not easy to produce edge chipping, which greatly improves the pass rate of subsequent processing.
In addition, in the polishing process, if the wafer is not chamfered, the sharp edge of the wafer will scratch the polishing cloth, which will affect the service life of the polishing cloth and the processing quality of the product (such as the scratch of the wafer). The wafer needs to be oxidized, diffused and lithography at a high temperature of more than 1000 degrees for many times in the multiple processes of manufacturing integrated circuits. If the edge of the wafer is not good, such as chipping or the edge is not chamfered, the internal stress of the wafer cannot be uniformly released during the heating and cooling process. The wafer is very easy to be broken or deformed at high temperature, and eventually the product is scrapped, resulting in greater losses. Due to the poor edge of the wafer, if the falling crystal slag sticks to the surface of the semiconductor wafer, it will cause damage to the lithography plate of the lithography process, and at the same time cause pinholes on the surface of the device and poor exposure, which will affect the yield of the product. At the same time, the wafer diameter can be standardized by edge chamfering.
Usually the diameter of the wafer is controlled by the rounding process. Due to the limitation of the precision of the rounding equipment, the surface roughness and diameter cannot meet the customer’s requirements. The chamfer process can well control the wafer diameter and edge roughness.
2. What Affects the Edge Quality during the Chamfer Process?
There are many factors that affect edge chamfering, mainly including:
* Selection of cams;
* Wafer center positioning accuracy;
* Wafer Mounting Flatness
* High and low speed, stability
* Verticality when rotating at high speed;
* Abrasive grain size of the grinding wheel, etc.