|
Characterization of semiconductor materials has been rapidly enhanced by the application of photoluminescence and laser-Raman spectroscopy. Photoluminescence is uniquely suited for identifying impurities as well as mapping whole wafers to determine the distribution of dislocation densities or impurity clusters over the surface. Assessment of subsurface damage is also possible. Such data has been correlated with the threshold voltages of finished devices. Laser-Raman spectroscopy, on the other hand, will identify surface contaminants and determine lattice disorder, residual strain and free-carrier density. Separate, dedicated instruments are typically employed for each type of investigation, In this paper, the authors present an automated system that delivers both photoluminescence and Raman capabilities. Wafers up to 4 inches in diameter were characterized at room temperature and while cooled by liquid helium. Sample materials included Si, AlGaAs, GaAs, LiNbO and In?. Information from spectra, wafer maps and peak shifts is presented and discussed. The quality of semiconductor devices and their mass-production yields depend largely on how well the materials from which the devices are fabricated can be characterized. Equally important is the effect of processing upon these materials. Currently, optical spectroscopy is emerging as a primary source of such information for both fundamental research and quality control in manufacturing. The non-contact and non-destructive nature of optical spectroscopic analyses is one of the most attractive reasons for the popularity of these characterization techniques. Capable of being fully automated through microprocessor control, optical spectroscopy also generates a range of data unmatched by other methods. And among the spectroscopic techniques currently available, photoluminescence and Raman spectroscopy are especially effective for characterizing semiconductor materials like silicon, gallium arsenide or indium phosphide. In its most basic form, photoluminescence (P1) involves exciting a sample with photons for higher energy than the semiconductor's band gap and observing any emission that results. In addition of providing a measure of crystal quality, photoluminescence has been used extensively to study the role of dopants in the production of Si, semi--insulating GaAs and InP. In the evaluation of ion-implanted III-V semiconductor, photoluminescence has been employed to map the distribution of impurities, surface degradation from implantation and annealing, as well as lattice reconstruction during annealing. Raman spectroscopy complements photoluminescence characterization by providing a more comprehensive structural and molecular picture of semiconductor materials . The important parameters of a Raman semiconductor spectrum are the peak position and line shape of the longitudinal optic (LO) and transverse optic (TO).
|
