What are Silicon Wafer Crystalline Defects?
Crystalline Defects In Silicon Wafer
The task is to make a single crystal silicon wafer with only one crystal with a defect free of a region on it, and this is the subject of the present invention and has the potential to be used in high-performance electronics and other electronic devices such as computers and televisions. This should facilitate the formation of fault-free regions and the securing of the electronic circuits on silicon wafers. [Sources: 5, 8]
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Silicon Wafer Crystalline Defects
Crystalline defects are irregularities of normal crystalline patterns in solids. They occur most frequently in organic solvents because of their high rate of vaporization. They are very common in polycrystalline compounds, where crystal lattices exhibit a repeating periodic crystalline structure, and are therefore common in materials such as glass, ceramic, porcelain, and quartz. Their appearance is sometimes called "cavity streaks" or "icing". Since defects often cause an excess of crystalline surface area that contacts the substrate, the defects can be quite pronounced and costly to remedy. They are therefore important to mechanical testing.
Crystalline vacancies are most common in quartz. Although impurities cannot be seen, visual inspection shows areas of higher stress concentration, due to crystalline movement. Most impure vacancies have no influence on the mechanical properties of a material, but when defects cause a granule dislocation within a quartz piece, the stress concentration in the interior can be high enough to dislodge a particle. This process can be used in many industries to increase fatigue life, reduce tensile strength, and create a smooth surface. Other uses include bumpers in sealants, slots and ramps in electronic devices, and mechanical fasteners in brazing.
Most defects found in crystalline materials are caused by a minor contact barrier between the substrate and crystalline interface. This is referred to as a "dipole moment". A much larger area of free liquid is found between the two interfaces than is the case with regular crystalline structures, because the free liquids usually do not contain a significant amount of crystalline structure. The contact is usually too weak for a significant amount of energy to transfer from the substrate to the defect. The crystals usually respond by growing into the gap, pushing the substrate out. The process of crystallization causes the flaws, or crystallites, that are found as defects in the material.
Crystalline defects, when present, must first be allowed to grow and then be fixed. It may be very difficult to identify mechanical properties of a crystalline sample that have been changed due to the reaction of the substrate with the impurity. Crystalline growth in itself is random, so it can sometimes be hard to judge the mechanical properties that are affected by the process. Most defects will return to their original mechanical properties after the substrate has passed through the impurity.
Some common crystalline defects include buckling, flaking, and lamination. Buckling occurs when the stress applied to the sample causes a microscopic crack in the material, allowing water to seep through. If the crack is located near the surface of the crystal, the surface tension of the liquid may cause the crystal to bulge, forming a visible defect.
Flaking is the most common of the defects, and occurs when there is a low or high salt content in the sample. Because of this, the sample becomes saturated with salt before the impurities are absorbed. Once the sample is cooled below the equilibrium level, the excess salt drops from the sample onto the surface, forming a lamination. This is a very common defect and can be detected with a refractory test.
Crystalline or parasitic texturing is often mistaken for porosity, as it is both physically and chemically diverse from porosities. However, texturing occurs when the crystal is exposed to a high salt concentration, causing the material to change from a solid to a semi-solid. When the process is slow enough, it can form a layer on the surface of the crystal that is identical to the rest of the material. This makes it appear as though the surface has no pores, but when high enough, it allows small leaks to develop.
Crystalline defects in materials range widely in both depth and width. Some examples of these defects include amorphous, cycloidal, dipteranoid and mixed. The amorphous variety displays irregular crystals which tend to look like a honey comb, while cycloidal displays irregular stripes of waxy substances. These irregular forms are produced by random crystallization.