Process Physics of the Iron-Boron Pair Recombination and Dissociation in p-Type Silicon
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PROCESS PHYSICS OF THE IRON-BORON PAIR RECOMBINATION AND DISSOCIATION IN p-TYPE SILICON W. WIJARANAKULA
Research and Development Department, SEH America, Incorporated 4111 Northeast 112th Avenue, Vancouver, Washington 98682-6776, USA ABSTRACT The process physics of the iron-boron pair recombination and dissociation in p-type silicon at temperatures below 300"C was studied. The result indicates that the recombination and dissociation processes depend strongly upon the relative position of the ionization energy of interstitial iron E.,' and the Fermi level EF. At temperatures T < (EFv+- E1 )/k, the pairing reaction obeys first-order reaction kinetics while at temperatures T > (EF+ - E)/k, an equilibrium between neutral and charged defect species prevails. INTRODUCTION In semiconductor silicon technology, transition metals, particularly iron (Fe), introduced during wafer processing and device fabrication causes either structural damage to the integrated circuit (IC) device or degrades minority-carrier lifetime [1]. The lifetime of minority-carriers in silicon is an important parameter because it directly determines the performance of the IC devices, such as dynamic random access memory (DRAM). It is well recognized that the removal of iron from the device active region using the conventional gettering process is considerably difficult because iron tends to precipitate at the silicon surface [1] due to its low thermal equilibrium concentration and high diffusivity. In addition, the charged Fe impurities interact with ionized boron atoms via a FeB pair formation and are gettered at the heavily-doped region of the IC device such as the field oxide isolation [1]. The FeB pair introduces a defect level which contributes to an increase in the current leakage of the n~p junction. Therefore, the elimination of defects associated with interstitial Fe from the device active region in p-type silicon requires a good understanding of both the behavior of interstitial iron and the process physics of the FeB recombination and dissociation. THEORETICAL Theoretically, the reaction kinetics of the FeB pair formation and dissociation in p-type silicon containing Fe can be described by the expression Fe* + B_ -,- (FEB)°1+
(1)
A pairing reaction in Eq.(1) is facilitated by the Coulombic attractive force and can take place even at room temperature (RT) due to the high diffusivity of the Fei+ species. The notation o/- means that the defect has the neutral charge state if the level is filled with an electron, positive charge state if empty. The transformation of the Fei+ species to the FeB
species obeys first-order reaction kinetics and the concentration of the Fei+ species as a function of time t at a given temperature can be expressed by [2]
(C+- C;')exp[-tD-,F V
- ND
C+ .q
Mat. Res. Soc. Symp. Proc. Vol. 262. 01992 Materials Research Society
(2)
S
562
where Cp,+ and C,,+q are the initial and equilibrium concentrations of the Fei+ species, respectively. D,, is the diffusivity of iron, expressed by 1.3xl0 3 exp(-0.68 eV/kT) cm2
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