Research on Single Crystal Silicon Stress Release Process

The slip distance of silicon wafer indentation dislocations at a certain temperature can be used to characterize the mechanical strength of silicon wafers. This method has low requirements for instruments and equipment and is simple and easy to implement, and has been widely used by people. When indentation is applied on a silicon wafer, compressive stress is left at the intact lattice while introducing dislocations. At a certain temperature, indentation dislocations in silicon wafers slip along the <110> direction under stress, forming specific patterns on specific crystal planes (such as (100) or (111) planes). In recent years, researchers use confocal microscopy Raman spectroscop method to study the magnitude and distribution of residual compressive stress in silicon wafer indentation, exploring  the influence of residual compressive stress changes in indentation on dislocation slip.

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1. Effect of Silicon Stress Pre-Release on Indentation Dislocation Slip

After being heat-treated for 2 hours at 300℃ (Fig.1 c) and 500 ℃ (Fig. 1 d), the stress changes of single crystal silicon wafers were observed. It can be seen that after the above heat treatment, the compressive stress near the indentation was released to varying degrees, and the 500℃ heat treatment released stress more significantly than the 300℃ heat treatment. In fact, after being treated at 500℃ for 2 hours, the indentation dislocations experienced a certain degree of slip, which intensified the release of stress.

Fig. 1 Microscopy image of silicon wafer indentation (a) and confocal microscopy Raman image (b: without preheating treatment; c, d: After heat treatment at 300 ℃ and 500 ℃)

After the stress pre-release caused by the low-temperature heat treatment mentioned above, the slip velocity of indentation dislocations significantly decreases during subsequent high-temperature (700-900 ℃) heat treatment;

The pre release of residual stress from indentation significantly reduces the slip velocity of dislocations;

When the residual stress after stress pre release is still greater than the critical stress required for dislocation slip at a certain temperature, the maximum distance of indentation dislocation slip remains almost unchanged, but the time required to reach the maximum distance is prolonged, and the degree of extension is related to the heat treatment temperature of stress pre release and the heat treatment temperature that causes dislocation slip.

Fig. 2 Changes in dislocation slip distance without preheating treatment and with preheating treatment

Red star location in b: slip distance of dislocations after 2 hours of heat treatment at 700°C without preheating treatment

2. Conclusion

In summary, the residual stress of indentation will be released to varying degrees during lower temperature heat treatment, and the higher the heat treatment temperature, the more significant the release of residual stress. After stress pre release caused by low-temperature heat treatment, the slip velocity of indentation dislocations significantly decreases during subsequent high-temperature heat treatment. However, as long as sufficient heat treatment is carried out, the maximum distance of dislocation slip is almost the same as that without prestress release.

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Reference:

Zhao Ze-Gang, Tian Da-Xi, Zhao Jian, Liang Xing-Bo, Ma Xiang-Yang, Yang De-Ren. Effect of prior stress-relief on the gliding of indentation dislocations on silicon wafers. Acta Phys. Sin., 2015, 64(20): 208101. doi: 10.7498/aps.64.208101