Lattice site investigation of F in preamorphized Si

Abstract

The lattice location of F atoms in Si was experimentally studied. Si single crystals were amorphized, implanted with F, and afterwards the amorphous layer was recrystallized. Some of the samples prepared in this way were also annealed at 750°C for 60 min. The 19 F͑p , ␣␥͒ 16O resonant nuclear reaction at 340.5 keV was employed to measure the probability of a close encounter between protons and F nuclei as a function of the incident angle with respect to six major crystalline directions. The predictions of several ab initio calculations proved to be incompatible with the present experimental findings. The miniaturization of complementary metal-oxidesemiconductor ͑CMOS͒ devices requires the confinement of dopants very close to the surface. In the microelectronics industry, the dopants are introduced through ion implantation. This technique is widely used because the depth and concentration of the dopant are easily controlled and reproduced. However, the implantation process generates point defects ͑self-interstitials and vacancies͒ in the target at a concentration well above the thermodynamical equilibrium level.1 These defects undesirably accelerate the dopant diffusion. This phenomenon is called transient-enhanced diffusion ͑TED͒, and it may be several orders of magnitude faster than normal thermal diffusion. TED is particularly dramatic for boron, 2 the most frequently used p dopant, hindering thus the further miniaturization of CMOS devices.In order to reduce the boron TED, coimplantation of F is currently used in the microelectronics industry, although the role F plays in the reduction of boron TED has not yet been entirely understood. To better understand the mechanism whereby F leads to a decrease of boron TED, substantial experimental and theoretical work has been carried out. Up to now, it is known that the slowing down of boron TED occurs by the interaction between F and point defects, and it has been suggested that F atoms form complexes with these defects. [3][4][5][6][7][8][9] By ab initio calculations, several authors 5,7,8,10 have found that the lowest-energy state for a single interstitial F in Si is at the bond-centered the ͑BC͒ site in the +1 charge state or at the tetrahedral ͑T͒ site in the −1 charge state, depending on the Fermi energy. However, in Refs. 5 and 7 it was obtained that fluorine-vacancy ͑FV͒ complexes are highly favored over the interstitial configuration. From the experimental standpoint, the detection of FV complexes by positron annihilation spectroscopy has been reported in Refs. 3, 4, and 9 and also through sheet resistance measurement in Ref. 6. On the other hand, electric quadrupole hyperfine interaction and preliminary channeling experiments have indicated that F might occupy either bond or antibonding ͑AB͒ interstitial sites. 11,12 In the present work, the lattice location of F atoms in Si was experimentally investigated. Czochralski n-type ͑P-doped͒ ͗100͘-Si single crystals with 10-20 ⍀ cm resistivity were amorphized from the surface down to a depth of about 440 nm wit...

Fluorine codoping in germanium to suppress donor diffusion and deactivation

“…In particular, simulation studies suggested that the most abundant F n V m clusters are those in which all the V dangling bonds are saturated by F. 16 Interestingly, recent experimental work 10 on F-implanted preamorphized Si determined that the predicted F n V m clusters do not exist in detectable concentrations. Nevertheless, that study 10 is consistent with theoretical work 14 as F implantation can effectively suppress the transient-enhanced selfinterstitial mediated diffusion of acceptor atoms such as B.…”

“…A number of experimental [9][10][11] and theoretical [12][13][14][15][16][17] studies address the issue of doping Si with F. These provide evidence that F n V m clusters are stable in Si. In particular, simulation studies suggested that the most abundant F n V m clusters are those in which all the V dangling bonds are saturated by F. 16 Interestingly, recent experimental work 10 on F-implanted preamorphized Si determined that the predicted F n V m clusters do not exist in detectable concentrations.…”

Toward Defect Engineering Strategies to Optimize Energy and Electronic Materials

“…Density functional theory (DFT) and experimental studies consistently revealed that isovalent codoping and double donor doping in Ge do not effectively reduce the formation of dopant-vacancy clusters that can lead to deactivation [63,64]. The introduction of fluorine in Si and Ge is motivated as it is a dopant that can passivate the dangling bonds formed by the vacancies [65][66][67][68][69][70]. The key is the high electronegativity of F and via the saturation of the dangling bonds, and it essentially immobilizes the lattice vacancies.…”

Vacancy-Fluorine Clusters in Silicon

“…Codoping in semiconductor materials is an efficient way to control the diffusion of dopants and control their electrical activation [1][2][3][4][5][6]. One of the most important materials where codoping strategies have been applied is Si [1][2][3][4][5][6][7][8][9][10][11][12].…”

“…One of the most important materials where codoping strategies have been applied is Si [1][2][3][4][5][6][7][8][9][10][11][12]. F atoms in Si saturate the dangling bonds of vacancies resulting in the formation of F n V m clusters, which in turn suppress the transient enhanced diffusion of B (Refs.…”