Dominant Influence of Beam-Induced Interface Rearrangement on Solid-Phase Epitaxial Crystallization of Amorphous Silicon

Abstract

Bombardment with 0.6-3-MeV Ne + ions has been employed to stimulate solid-phase epitaxial growth of amorphous silicon at temperatures 200-500 °C. Two distinctly different regrowth regimes have been identified. In the temperature range 200-400 °C the activation energy for beaminduced regrowth is 0.24 eV, whereas, in the temperature range above 400°C, it is higher (>0.5 eV), but less well defined because of competing thermal effects. Results indicate that ion irradiation generates (athermally) nucleation sites for crystal growth, a process which has a high ( ~ 2.4 eV) activation energy in the absence of ion-beam excitation.PACS numbers: 68.55.+ bAmorphous layers in the near-surface region of crystalline silicon recrystallize by solid-phase epitaxial growth (SPEG) when heated to temperatures of >500°C. 1 This process is characterized by an activation energy of -2.7 eV. 2 Phenomenological models of the SPEG process 3 "" 7 have been successful in providing a qualitative explanation for the dependence of the growth kinetics on both substrate orientation and concentration of dopants; however, details of the growth mechanism are yet to be determined, in particular the interpretation of the activation energy.Recently, it has been observed that SPEG can be induced in silicon at ambient temperatures in the range 200-500 °C by irradiation with energetic ions. 8 " 13 These studies have adequately demonstrated that crystallization is not a consequence of local beam heating but results more directly from ion-atom interactions in the substrate. However, the experimental conditions employed in these studies often precluded the identification of the factors responsible for beam-induced SPEG. In particular, the competition between damage production and crystallization induced by the ion beam often complicated the interpretation of results. 8,10,n In the present study, by simplifying the bombardment conditions we have been able to demonstrate the dominance of defect generation at the amorphouscrystalline interface in controlling SPEG. o We have studied SPEG of -1000-A-thick amorphous silicon layers produced in (100)-oriented single-crystal silicon samples, held at -77 K, by irradiation with 50-keV Si + ions to a fluence of 2.5 x 10 14 cm"" 2 . We have used 0.6-3-MeV Ne + -ion bombardment to stimulate SPEG. These high-energy ions penetrate to depths o of 0.95 to 2.5 jum, respectively. Over the first 4000 A of their penetration the ions lose energy at a nearly constant rate (<5% variation even in the 0.6-MeV case), so that the amorphous layers are uniformly excited throughout their thickness. Before neon-ion bombardment all samples were preannealed thermally at 450 °C for 15 min to remove partial amorphous regions and thus provide an abrupt crystal-amorphous interface for beam-induced SPEG studies. Both Ne + -induced crystallization and subsequent analysis of the extent of growth using 1.5-MeV-He + ion channeling and backscattering were performed in situ in a vacuum chamber operating at 10" 7 Torr. Samples were mounted on a two-axis...

Amorphization/recrystallization of buried amorphous silicon layer induced by oxygen ion implantation

“…Figure 1 presents the RBS spectra of samples submitted to IBIEC induced by a high temperature oxygen implantation performed to a fixed dose of 5ϫ10 16 cm Ϫ2 . The spectrum corresponding to the original amorphous layer created by the double implantation procedure described in the previous section is labeled as a ''Control sample.''…”

“…Czochralski-grown ͑100͒ silicon wafers of p-type conductivity, with resistivity of 8 -12 ⍀ cm, were implanted with 16 O ϩ ions at a fixed energy of 185 keV. According to TRIM 18 code simulation, the mean projected range (R p ) and standard deviation (⌬R p ) of these implants are 375 nm and 84 nm, respectively.…”

“…Subsequently, a nominal room temperature ͑RT͒ implantation to the dose of 4ϫ10 15 cm Ϫ2 was performed with the purpose of creating a buried amorphous layer. A set of samples was then submitted to oxygen implantation in the temperature range of 150-600°C, with doses varying from 2ϫ10 16 to 8 ϫ10 16 cm Ϫ2 . All the implants were conducted limiting the beam current density to the range of 1 -3 A cm Ϫ2 .…”

“…According to TRIM 18 code simulation, the mean projected range (R p ) and standard deviation (⌬R p ) of these implants are 375 nm and 84 nm, respectively. After cleaning, the wafers were implanted at 600°C to a dose of 5ϫ10 16 cm Ϫ2 . Subsequently, a nominal room temperature ͑RT͒ implantation to the dose of 4ϫ10 15 cm Ϫ2 was performed with the purpose of creating a buried amorphous layer.…”

“…7 The measured activation energies for the IBIEC process varies from 0.18 eV to 0.38 eV. 7,15,16 In the present study we consider the case where three sequential O ϩ implants, realized at the same energy, were accumulated in the samples. The first implant was performed at an elevated temperature, to maintain the material single crystalline, with a dose sufficiently high to establish a peak oxygen atom concentration of ϳ3 at.…”