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https://hdl.handle.net/2142/66257
Description
Title
Laser Annealing of Ion Implanted Silicon
Author(s)
Bhattacharyya, Anjan
Issue Date
1981
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
We present here a detailed theoretical and experimental investigation of the dynamics of surface melting and regrowth and electrical activation of Si('+) and BF(,2)('+) ion implanted amorphized silicon annealed with a Q-switched Nd:glass laser ((lamda)= 1.06 (mu)m). In the theoretical calculations we have used the technique of finite difference equations to solve the one-dimensional heat conduction equations for the solid and liquid phases. We have taken into account the temperature dependence of all the parameters involved to give us a realistic model. The melting model is supported by time resolved reflectivity measurements using a He-Ne and an Ar laser. We use SEM to investigate the electron channelling pattern to study the quality of crystalline regrowth. For BF(,2)('+) implanted silicon, the boron and fluorine atomic profiles are measured by secondary ion mass spectrometry (SIMS) on as-implanted samples as well as laser annealed samples. The impurity redistribution is explained on the basis of the melting model. Differential resistivity and Hall effect measurements in conjunction with successive layer removal are used to obtain the electrical carrier distributions as a function of the laser fluence. For good quality crystalline regrowth and full electrical activation, the laser fluence should lie between the melting threshold and the damage threshold. Therefore, a reliable model is useful in designing experiments of laser annealing.
Pulsed CO(,2) lasers ((lamda) = 10.6 (mu)m) have the distinct advantage of having considerably larger spot-size than a Nd:glass, YAG or Ruby Laser, and are therefore very promising for laser annealing of large Si wafers commonly used in industrial production. At 10.6 (mu)m, the absorption coefficient of amorphous silicon is much smaller than that of crystalline silicon having large donor concentration. Hence, for annealing with a CO(,2) laser it is advantageous to implant the sample with a moderately high ion dose without driving the sample amorphous.
We present a calculation of the temperature rise and investigate the "thermal runaway" phenomenon during pulsed CO(,2) laser annealing of silicon. The calculations are based on the thermal melting model, taking into account the temperature dependence of all pertinent material parameters, including the absorption coefficient. In calculating the temperature variation of free carrier absorption in n-Si, we have taken into account acoustic deformation potential scattering, optical deformation potential scattering, and ionized impurity scattering. The deformation potentials are adjusted to fit the experimentally observed values at 300(DEGREES)K.
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