Second-Harmonic Generation(SHG) Based On Femtosecond Laser To Detect Biaxial Strain Of Silicon Surface

As the characteristic dimension of semiconductor device goes into the nanometer,when the method of proportional reduce the size of device to improve chip speed encountered the obstacle cooling, quantum tunneling and physical limits, Strained Silicon technology bored. With the strained silicon technology deepening, people have realized it can effectively enhance the processing speed and performance of chip when introduce appropriate amount of strain silicon into the semiconductor device structures and materials. This technology has also attracts more and more attention of researchers and has been applied into the chip production. The introduction of small strain is the key of strained-silicon technology, so we must be looking for such a method which can measure this small-scale stress and strain accurately.In the field of semiconductor chips, there are usually two broader strain measurement technologies, which are Raman spectroscopy and convergent beam electron diffraction. However, there are obvious shortcomings when they measure the device structure. So we select the method of Second-Harmonic Generation (SHG) to measure the strain in this experiment. SHG is an optical non-contact method, it has no destruction to the sample, not any pollution to the environment, and very sensitive to the nature of the surface and interface. And also it is available in real-time measurement and in situ measurement techniques.Now SHG approach has been widely used to characterize the nature of Si surfaces and interfaces, SHG method can be characterized with the oxide layer-related information, such as Si surface oxidation kinetics, oxide thickness and so on. It can distinguishes ?-level interface roughness, and measures silicon atoms arranged in the interface configuration. SHG method can also reflect changes in the interface strain, but previous studies have only produced during the annealing out of strain changes can be seen by the size of SH intensity without specific size of the measured strain. This is what we should study the contents of the laboratory. In this work we completed the measurement of the biaxial strain of silicon surface with SHG based on femtosecond laser.This paper describes the application of strained silicon technology. This paper reveals the principle of biaxial strained silicon technology, and the effect of introducing biaxial strain to the device on the silicon lattice structure, band structure and carrier mobility.In the first part of the experiment, we measured the curve of SH intensity under different polarization changes with the Si film azimuth. The curve has six fold symmetry under the S-in/S-out polarization. And the curve has triple symmetry under S-in/P-out polarization. These two sets of curves can reflect the anisotropy of Si crystal lattice structure and configuration of surface atoms. The surface atoms with C3v symmetry.In the second part of the experiment, we designed and produced two kinds of device which can impose mechanical biaxial tensile stress and biaxial compression stress on the circular Si films. We measured the curve of the SH intensity changes with the Si azimuth under the stress induced in the case of biaxial compressive strain, and discover polarized SH intensity decreased uniformly throughout the range. And we choose to measure the applied biaxial strain curve at the peak of SH intensity, and find out SH intensity strengthen with increase of the applied biaxial tensile strain. SH intensity decreases while the applied biaxial compressive strain increases until the strain reaches a minimum value, and then it increases reverse. The minimum is what we want to measure--the Si surface strain. Its size is aboutε_xx =ε_yy=ε₀ =3 .07×10^-4. At last we achieve the calibration of a biaxial strain on the Si surface.