Raman And RBS Studies Of Ion Implanted Semiconductors

ABSTRACT Raman spectroscopy and Rutherford backscattering spectrometry (RBS) have been used to assess boron and silicon implants on the properties of single crystal silicon, GaAs, and CdTe. The behavior of these different semiconductors under identical implant conditions has been compared. Changes in the Raman optic phonon spectra reflect the extent of lattice damage caused by the ion implants as well as ability of various annealing pro­ cedures to remove this damage. The Raman results are generally confirmed by RBS ion- channeling measurements. Furthermore, these techniques are shown to provide complementary information on the distribution and nature of implant damage. 1. INTRODUCTION Raman spectroscopy is based upon the inelastic scattering of light by matter. Although numerous physical mechanisms can generate Raman scattering (RS) in solids,1 the electron- phonon interactions associated with lattice vibrations normally provide the most universal means to characterize structural and chemical properties. RS has been widely used to evaluate the composition, crystalline order, and lattice strain in bulk and thin film semiconductors.^ Since RS measurements are generally nondestructive (as long as damage from the probe laser beam is avoided), they can be integrated into device processing procedures to observe the effects of specific treatments on structural, optical, and electrical parameters of the semiconductor. Of course, there are limitations1' 2 on the sensitivity and uniqueness of the RS results, but in favorable cases (which can occur with many elemental and compound semiconductors) remarkably detailed information can be obtained.2 One technology area where RS is particularly useful is the behavior of semiconductors to energetic ion implants. RS is often able to monitor the degree and nature of structural disorder produced by the implants as well as the recovery of crystal- linity and electrical activation of deposited atoms following post-implant anneals by various methods. Examples of RS characterizations of ion implanted diamond and zincblende structure semiconductors abound in the recent literature.3-14 in some cases the site occupancies of the implanted atoms can be established by localized vibrational modes (LVM) in the Raman spectra.^'10' 12' 13' 15In order to better understand the microscopic processes associated with ion implantation technology in semiconductors, a variety of experimental methods that monitor structural, optical, and electrical properties are being applied to different semiconducting materials following simultaneous implants. Raman scattering has had a prominent role in these studies. The present paper describes some of the results on the effects of heavy dose boron implants and subsequent thermal anneals on single crystal silicon, GaAs, and CdTe. In particular, the influences of ion kinetic energies, fluence, and sample temperature during the implant have been examined by RS measurements. Interpretations of the Raman data have been greatly facilitated by Rutherford backscattering spectometry (RBS) - ion channeling results that were obtained on identical samples. RBS channeling can provide much information1^ on the structural disorder induced in single crystals by ion implant­ ation as well as the effectiveness1^' 1^ of post-implant processing to remove the damage. In the present work, the complementary nature of the Raman and RBS methods have proven to be extremely beneficial in the evaluations of the implanted and annealed samples. The relationship between these two techniques will be the primary focus of this paper. Detailed assessments of ion implantation on the individual materials that have also incorporated results from other analytical and spectroscopic methods will be presented elsewhere.