Analysis Of Metal Diffusion In Silicon Wafers By Laser-induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a full-elemental analysistechnology. In recent years, LIBS-based application is still concerned by people.Currently, this technology has been widely used in industrial production, enviro-nmental monitoring, biomedicine, and other fields.In semiconductor silicon industry, metals are always deposited on the surface ofsilicon wafers to structure transistors. During the progress of forming transistors,metals often diffuse into the silicon wafer which can weak the electronic performanceand even lead to failure of the transistors. At present, silicon chips are analyzed at theend of the process of manufacture, and the analysis process always takes several daysand needs a series complex sample preparation. Silicon chips not conforming to thecriteria mean elimination which leads to the waste of time and material. At present,there is no mature and standards silicon material analysis in domestic. LIBS techniqueitself has advantages of fast, efficient, Simultaneous detection of multiple elementsand etc. Therefore, laser induced breakdown spectroscopy (LIBS) proposed to be usedfor the analysis of metals diffusion in silicon wafer as a useful diagnostic tool ispresented.In our previous work, the impurity P and O in silicon was detected by LIBS invacuum environment. The detection environment is strict and the versatility is notstrong. Therefore, the detection of this time is achieved at atmospheric environment.As there are many factors that affect the accuracy at atmospheric environment forLIBS, this paper firstly analyzed the impact of environmental pressure in LIBSdetection by experiment. Experimental results indicate that changes in air pressurewill affect the temperature of the plasma, thereby affecting the strength of ion andatomic peak ratio in sample. Moreover, the weak changes in air pressure can alsoaffect the accuracy of laser-induced breakdown spectroscopy quantitative analysis.Then we improved the stability of the detected ambient pressure, using LIBSsystem to detect the metal profiling in silicon wafer. The sample in experiments wereprepared with Al, Zn, Mn, Ge thin film on silicon wafer, and using high-temperatureto stimulate the metal diffusion in silicon. In the experiment, a detailed analysis of theAl diffusion depth of Al-Si is presented. In addition,3other samples were alsodetected by LIBS. For the effect of several sample’s detection analyzed theapplicability of LIBS in silicon metal diffusion test. In the test of sample Al-Si, the EDS technique cannot distinguish the differenceof Al concentration in higher depth of different samples due to the low detection limit.On the contrary, the use of laser-induced breakdown spectroscopy can clearly disti-nguish the diffusion depth of different sample. The results illustrate that the LIBStechnique is very suited for the detection of Al diffusion in silicon wafer.The experiments also analyzed the metal diffusion of Sn, Mn, Ge in silicon atdifferent annealing temperatures. From the experimental results, the effect of Sn-Sisamples tested well and can clearly distinguish the difference between theconcentration of elements at different depths. However, the Mn-Si sample test is notideal, the test is almost undetectable. For the test of sample Ge-Si, although only afew of the characteristics spectrum peaks that can distinguish, but the distribution inthe depth test can also have a certain resolution.Finally, for the experimental results, the applicability of using LIBS technique todetect metal diffusion in the silicon was discussed.