Double-hump diffusion profiles of copper and nickel in germanium wafers yielding vacancy-related information

Abstract

Diffusion of Cu and Ni into Ge was investigated between 700 and 900 °C with the aid of rapid isothermal lamp annealing and spreading-resistance profiling. Using low-dislocation-density single-crystal Ge wafers with a backside gold layer, we observed typical double-hump diffusion profiles of both Cu and Ni. These profiles can be described within the dissociative model by taking into account that the front surface acts as source for both vacancies (V) and Cu or Ni while the back surface combines the V-source feature with a Cu, Ni-sink property. Profile fitting yields data regarding the V-assisted Ge self-diffusion coefficient and the equilibrium concentration of vacancies as a function of temperature.

Diffusion ofn-type dopants in germanium

“…Studies on Cu precipitation in Ge and on thermally induced acceptors formed after quenching reveal a V formation enthalpy of about 2 eV. 24,[67][68][69] Metal diffusion studies of Giese et al 25 support the results of the former quenching experiments. Recently, Vanhellemont et al 26 report a best estimate of (2.35 6 0.1) eV and (0.6 6 0.1) eV for the formation and migration enthalpy of V, respectively, which is based on available experimental and theoretical results.…”

“…Understanding of their properties is necessary to control the diffusion and electrical activation of dopants. [22][23][24][25][26][27][28][29][30][31][32][33][34] Earlier investigations of Werner et al 22 determined that V mediate self-diffusion in Ge under equilibrium conditions. Under such conditions the concentration of native defects is in thermal equilibrium.…”

Direct observations of the vacancy and its annealing in germanium

“…Various authors have performed quenching experiments to determine the formation energy of the singly negatively charged vacancy. 6,[15][16][17][18][19][20] All of these studies find a formation energy close to 2 eV. It should, however, be noted that almost all the estimates above are based on indirect spectroscopic tools.…”

“…Among the fundamental properties that still needs addressing are migration and formation energies of point defects and their annealing temperatures. It has been established that in germanium the vacancy is the dominant diffusion-mediating point defect, both in self-diffusion [6][7][8][9][10] and impurity diffusion. 9,11 Some experimental work has been done on the determination of the formation and migration energies of the vacancy in germanium.…”

Lattice location and stability of implanted Cu in Ge

“…Possible candidates for dissociative diffusion are foreign atoms whose interstitial solubility is low but whose interstitial diffusivity very high, while their substitutional diffusivity is very low and their substitutional solubility moderate to high. The hypothesis by Frank and Turnbull regarding the Cu diffusion in Ge was confirmed by various authors with increasing experimental accuracy [2][3][4][5]. A striking consequence of the Frank-Turnbull diffusion mechanism is that the substitutional Cu-concentration in intrinsic Ge effectively maps the Ge vacancy profiles and can hence be used to extract information on the diffusivity and solubility of the Ge vacancy [5].…”