Evaluation of Semiconductor Lattice Damage Using a Newly-Developed Photodisplacement Laser Probe
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EVALUATION OF SEMICONDUCTOR LATTICE DAMAGE USING A NEWLY-DEVELOPED PHOTODISPLACEMENT LASER PROBE S.SUMIE*, H.TAKAMATSU*, H.TSUNAKI*, YNISHIMOTO* AND YNAKAI**
*Kobe Steel, Ltd., **Leo Corporation, 1-5-5 Takatsukadai Nishi-ku, Kobe, Hyogo 651-22, Japan ABSTRACT A highly sensitive laser probe for photo-acoustic displacement(PAD) has been developed and applied to the monitoring of low-level lattice damage in semiconductors. Since a photodisplacement laser probe with the sensitivity of 0.1 picometers is employed in this measurement, lower density damage for instance, formed by 50 keV B+ implantation with a dose of 5X1O0 ions/cmi can be detected. Correlation of the PAD with damage density was obtained in B+ implantation. Therefore, quantitative damage density can be obtained from the relation for lightly damaged layers, such as formed by chemomechanical polishing and by electron cyclotron resonance plasma etching. This technique is useful-for monitoring of low damage density surface. INTRODUCTION In the manufacturing process of very large scale integrated circuits (VLSI) with a below-half micron design rule, lattice damage, such as distortions and defects, is expected to be minimal. This is true not only for incoming wafers, but also after the wafers have been polished or etched. Evaluation of lattice structures of silicon, therefore, has become very important, and so there is a strong requirement for a surface characterization means with good sensitivity. The conventional methods for monitoring lattice defects include Rutherford Backscattering Spectroscopy(RBS)[1] for displaced atom density(DAD) measurement, X-ray topography[2], infrared photoelasticity_[3] preferential etching[4], X-ray rocking curve[5], and X-ray diffuse scatte nng[6] for characterization of damaged silicon surface. However, these techniques have been of limited use due to complexity or lack of sensitivity. AI though Thermal Wave technology, which detects the modulated reflectance with an optical probe, is a usefll method[7], technique with a higher sensitivity to detect the presence of low-level lattice damage is still desirable. The authors have developed a highly-sensitive photodisplacement laser probe, which detects photo-acoustic displacement(PAD) generated by a focused, intensity-modulated laser beam[8]. Recently, it has been realized that this new noncontact and nondestructive technique is very sensitive to the presence of lattice damage in the surface layer oT a silicon wafer, and it has been applied to monitor low-dose ion implantation down to 2X10 9 ions/cm 2[1]. This paper describes the application and feasibility of this technique to the monitoring of low-level lattice damage caused by low-dose implantation intrinsic residual damage of virgin wafers and ECR-plasma etch induced damage. EXPERIMENTAL APPARATUS AND PRINCIPLE The block diagram of the PAD measurement apparatus is illustrated in Fig.l. A beam of a 30 mW semiconductor laser(LD,p=780 nm) is employed as an exciting beam. The LD beam is intensity-modulated by adjusting the injection
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