Wafers are divided into Bare Wafer and Patterned Wafer, as shown in Figure 6. The starting point for considering the defect types of two types of wafers is somewhat different. There are many types of defects on the surface of wafers, which may be caused by processes or defects in the material itself. Using different defect detection methods may result in different classifications of defects. Taking into account the physical properties of defects and the specificity of subsequent defect detection algorithms, defects can be simply classified into surface redundancies (particles, pollutants, etc.), crystal defects (slip line defects, stacking faults), scratches, and pattern defects (for pattern wafers).
Surface redundancy
There are various types of redundant materials on the surface of wafers, ranging from tiny particles as small as tens of nanometers, to dust as large as hundreds of micrometers, and surface residues left by the previous process. Particles may be introduced through processes such as etching, polishing, cleaning, etc. Redundancy defects mainly come from dust on the wafer surface during production and processing, air purity not meeting standards, and chemical reagents during the processing. These particles can block light during photolithography, causing defects in the integrated circuit structure. Contaminants may adhere to the wafer surface, resulting in incomplete patterns and affecting the electrical characteristics of the chip, as shown in Figure 7.
Crystal defect
Slip line defects are also a common type of defect caused by uneven heating during crystal growth. They usually form small horizontal lines at the outer edge of the wafer. Due to the relatively large size of the slip line, it can be identified through manual observation.
Stacking faults are also defects that can be found in epitaxial layers, usually due to the disruption of the normal stacking sequence of the densely packed planes in the crystal structure, with sizes typically in the micrometer range.
Mechanical damage
Mechanical damage generally refers to scratches on the surface of a wafer caused by polishing or slicing, usually caused by chemical mechanical polishing (CMP), forming an arc shape, or it may be non continuous point distribution, as shown in Figure 10. This type of damage varies in size and usually affects the connectivity of the wafer circuit, making it a serious defect. This defect can be corrected, but it may be due to improper mechanical operation.
