| The study of acceptor Ga open-tube diffusion in SiO2/Si has been carried for several decades, whose pursuing was only to get the diffused surface of high uniformity and reproducibility and impurity distribution in Si which can improvethe electrical performance of the devices, but the various manifestation of Ga segregation effect at the SiO2-Si internal interface and the dynamic intendancy of the impurity concentration variability have not been reported. In order to comprehensively understand the diffusion mechanics and the distribution of Ga, which can provide theoretical basis for the further application of p-type impurity Ga in the new sub-micron devices and power electrical devices, the segregation effect and dynamic concentration profile of Ga at SiCb-Si internal interface have been investigated by several analytical methods such as secondary ion mass spectroscopy(SIMS),through which the new regulations of Ga segregation are found.In the first part of the thesis, the principle of Ga diffusion, the structure and the feature of the SiO2-Si internal interface, and the research of Ga doped in Si are summarized. Based on the analysis of Ga doping application in microelectrical and power electrical fields, the prospective of Ga is presented. Though open-tube Ga diffusion in SiCVSi has predominant superiority, its theory is not perfect enough to give systematical explanation to some problems in application, such as negative resistance effect.The second chapter discusses the oxidation and diffusion systems and the process of our experiment. Ga pre-diffusion and redistribution are conducted to n-type silicon with 200nm SiOi film, and two group samples, A and B ,are acquired; then following re-oxidation are carried:(l)original group A ;(2)group A with the SiOi etched;(3)original group B ;(4)group B simulating with phosphorus diffusion. Impurity Ga and the carrier concentration distribution are measured by SIMS and spreading resistance profile(SRP) spectroscopy individually.The segregation of Ga at SiO2-Si internal interface has been investigated systematically in the third chapter. The diffusion regulations of Ga under constant source in SiO2/Si are found: (a)Ga diffusion in SiCh follows Pick's First law, and the concentration-step increaseswith diffusion time under the same temperature;(b)Ga diffusion in silicon basically follows the error-function, and the surface concentration increases with diffusion time before the solid solubility is reached;(c)the concentration profile of Ga in SiC>2 is controlled by the segregation coefficient m ,where m is found not to be constant, but increasing rapidly with the surface concentration of Si, in another word, it is the function of diffusion temperature and time.During the redistribution protected by N2, Ga manifests the character of back-diffusion, whose current profile in SiC>2 follows Pick's law also; at the same time, Si3N4 nano-film is formed at SiOi-Si interface.The segregation under three re-oxidation conditions is studied:(l)sample with SiC>2 of shallow junction and high concentration;(2)sample without SiO2;(3)sample with SiCb of deep junction and low concentration. The following results are acquired: (a)the Si surface concentration decreases while the width of the exhausted region increases with the oxidation time;(b)the segregation Ga at SiO^-Si interface is predominated by DSl02/DSl ;(c)the degree of segregation is pertinent to the sample condition before re-oxidation and the oxidation rate, subsequently the segregation degree of (l)(2)(3)drops successively;(d)as long as the sample diffused with Ga is delt under oxidative condition, the corresponding segregation will happen;(e)the mathematical formulas of Si surface concentration changing with re-oxidation time under three conditions are deduced.The carrier concentration near base-region has a feature of three-phase after simulated phosphorus diffusion, and the relation between the carrier concentration near base-region and diffusion time of phosphorus is acquired. |
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