Deactivation of ultrashallow boron implants in preamorphized silicon after nonmelt laser annealing with multiple scans

Abstract

Electrical activation and redistribution of 500 eV boron implants in preamorphized silicon after nonmelt laser annealing at 1150°C and isochronal rapid thermal postannealing are reported. Under the thermal conditions used for a nonmelt laser at 1150°C, a substantial residue of end-of-range defects remained after one laser scan but these were mainly dissolved within ten scans. The authors find dramatic boron deactivation and transient enhanced diffusion after postannealing the one-scan samples, but very little in the five-and ten-scan samples. The results show that end-of-range defect removal during nonmelt laser annealing is an achievable method for the stabilization of highly activated boron profiles in preamorphized silicon. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2385215͔The continued downscaling of complementary metaloxide-semiconductor devices requires ultrashallow and abrupt source/drain extension regions with a low sheet resistance.1 Among the other processes nonmelt laser annealing has gained attention as a means of achieving these requirements by its short process time and high annealing temperature, and hence low thermal budget, resulting in high dopant solubility.2-5 A problem exists with creating highly active profiles when boron is implanted in conjunction with a preamorphizing germanium implant; deactivation occurs during postactivation thermal processes. [6][7][8][9][10][11][12] This deactivation is thought to be driven by the release of silicon interstitials from end-of-range ͑EOR͒ defects that evolve through nonconservative Ostwald ripening during annealing. 13 The interstitials flow towards the surface and decorate the boron profile, producing boron interstitial clusters. [14][15][16][17] In this letter, multiple laser scan annealing at 1150°C followed by isochronal rapid thermal postannealing at lower temperatures is used to investigate the role of end-of-range defects in the redistribution and deactivation of ultrashallow B profiles in preamorphized and nonmelt laser-annealed silicon.N-type ͑100͒ Czochralski-silicon wafers were preamorphized with 5 keV Ge + to a dose of 1 ϫ 10 15 cm −2 producing a surface amorphous layer to a depth of ϳ15 nm. 500 eV B + was implanted into the amorphous layer to a dose of 1 ϫ 10 15 cm −2 . Both implants were made using an Applied Materials Quantum X implanter. The wafers were exposed to a scanning diode laser source operated under nonmelting conditions, which was used to anneal three strips across the wafers, corresponding to one, five, or ten scans at a temperature of 1150°C. By using multiple laser scans to anneal the wafer, it allows a study of defect evolution as a function of increasing the thermal budget. The amorphous layer regrew by solid phase epitaxial regrowth during the annealing. Samples were taken from these strips and annealed in dry N 2 for 60 s at temperatures ranging from 700 to 1000°C using a Process Products Corporation rapid thermal annealing system operating with a 50°C/s heating ramp rate. The van der Pauw technique was use...

Extended Defects Formation in Nanosecond Laser-Annealed Ion Implanted Silicon

“…In contrast, the much shorter duration time of excimer laser annealing (<200 ns) is comparable to that of some basic point-defect related phenomena, such as Si interstitial diffusion and clustering 11 , which makes the defect-formation mechanism itself questionable in this annealing regime. In addition, most of the existing studies of defect formation in laser annealed silicon have been carried out in preamorphised structures: (i) after non-melt anneals, conventional endof-range defects ({311} defects and {111} DLs) have been observed [12][13][14] ; (ii) in the case of melt laser annealing, the defects nature depends on the position of the melt front with respect to the amorphous/crystalline, a/c, interface (stacking faults are observed in the case of incomplete melting of the preamorphised layer, 15 defect-free crystalline silicon is found when melting goes beyond the a/c interface 16 ).…”

Surface proximity and boron concentration effects on end-of-range defect formation during nonmelt laser annealing

“…6 This approach has been proven in practice to reduce EOR defect density and TED. 7 In this letter, submelt laser annealing is employed in a different approach where EOR defect behavior during laser and further annealing is investigated when the position of the a / c interface is adjusted with respect to a B implant.…”

Surface Heat Treatment of Silicon Wafer Using a Xenon Arc Lamp and Its Implant Activation Applications

“…Deactivation of implanted B and As activated by high temperature annealing during subsequent annealing steps is well known. [22][23][24] It is thought to be driven by the release of Si interstitials from end-of-range (EOR) defects. Suppression of deactivation nuclei is equally important as is the enhancement of electrical activation of dopants.…”