Optical Second Harmonic Generation Method for Silicon Material Monitoring and Characterization During Ion Implantation a
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affect the degree of success or failure of the transistors. Nevertheless, ion implantation monitoring has been difficult since most existing techniques are either incapable of in situ application or lacking the sensitivity required. Optical second harmonic generation method is non-destructive, capable of in-situ and real time applications, and it has also shown high sensitivity in surface studies[ 1]. Thus the SHG technique may meet the requirement for process monitoring during the integrated circuit manufacturing. In this paper, we report our preliminary work in applying the technique to ion implantation and thermal annealing process monitoring. In the following, we will first describe the technique and the physics it is based on. Then we will show the results of SHG measurements, along with TEM observations, for silicon materials that have been treated with phosphorus ion implantation and rapid thermal annealing (RTA), and we discuss the results as well as the potential of using the SHG technique for integrated circuit process monitoring. THEORY AND EXPERIMENT Non-linear optical second harmonic generation is the phenomenon that, when a high intensity laser beam is shone onto a material, light with a frequency twice the incident laser beam (the second harmonic) will be generated from the material. The SHG set-up used in our experiment is shown in Fig (1). A Nd:YAG laser is used as the pumping source, with a beam diameter about 2 mm. The laser is mode - locked at a frequency of 76 MHz and it is also 95 Mat. Res. Soc. Symp. Proc. Vol. 406 ©1996 Materials Research Society
simultaneously Q-switched at a repetition rate of 1 kI-z. A half wave plate is used to change the polarization of the source beam. The sample is mounted on a rotation stage. A series of filters are used to make sure only the second harmonic signal from the sample is detected, and a polarizer is used to select the polarization of the second harmonic signal. The SHG signal is detected with a photomultiplier tube and gated electronics, and is recorded while the sample is rotated. The laser incident angle ý, sample rotation angle 0, and the incident laser beam polarization angle y are defined in the inset figure.
Nd:YAG Laser
X/2 plate
S= filter 2w filters PMT
Sample
Electronics
[COMPUTER
polarizer
Fig. (1) Experimental set-up for SHG measurement One fundamental theorem concerning optical second harmonic generation is that the most important term contributing to SHG - the electric dipole contribution - is zero for materials with centro-symmetry. This includes lattice structures with inversion symmetry, such as the diamond structure of silicon, or amorphous material such as silicon dioxide. Other terms that contribute to optical second harmonic generation do exist, but they are normally very weak. Mathematically, optical second harmonic from the electric dipole term can be described as follows[2]:
c1 LEI_ FE
d12 [d 11
2[E] jC[d2t Z
d22 d32 1
3
FE 1 d13 d14 d15
d16 ]
d23 dd24 d d25
d 26 - 2EE
d
33
d34
35
d36
Ed3 2 I2EE1 2x.
[2ExE
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