Research On Meta Interconnection Electromigration Token Methods Based On Noise

Since integrate circuit was invented, electromigration in metal interco nnection hasalways been an important restrictive factor for circuit reliability upgrade. Nowadays,Microelectronics devices continue miniaturization, circuit packaging tends to denseness,the section area of interconnection is smaller and smaller, the power density it takesincreases dramatically, thereby, interconnection failure caused by electromigration hasbeen the key issue in integrated circuit reliability research.How to characterize electromigration with sensitivity, accuracy, all-sided tokenparameters is the basis of electromigration research. With the advancement of technicsand reliability requirement, traditional token methods presents some limitations, such as,the mean time to failure(MTTF) can deal with a batch of samples but can not charac terindividual sample through failure mechanism; in-situ test method is intuitionistic, butthe samples need special preparation, it can not be used to reflect electromigration inworking statement; resistance test is simple and convenient, it can reflect the voidnucleation, however, it is insensitive to electromigration forepart damage and latentdefects. Therefore, new token techniques and parameters which more sensitive anddirectly relate to electromigration failure mechanism are needed.Noise as a new token method, was used more and more extensive in electronicmaterial and devices reliability research. The main advantages lie on:1) noise isnon-destructive;2) noise has a higher sensitivity;3) noise testing is simple, and theequipments don’t cost a lot;4) the establishment of noise models are relatively easier.This paper applied noise to electromigration failure characterize, presented a lowresistance interconnection noise test system, established a grain boundary free volumenoise model, executed electromigration aging experiment, extracted electromigrationnoise frequency spectrum parameters, analysed electromigration failure mechanism.Furthermore, electromigration process is a complicated dynamic process, its noisepresents some special properties, such as nonnormality, instability, complexity,singularity and chaos etc.. In order to characterize electromigration morecomprehensive and deeper, several time series analysis methods were also adopted. Themain innovation and production of this paper lies on:1．Aimed at the shortage of traditional noise testing system in low-resistance test, anew double-amplifiers-in series electromigration noise testing system was proposed. The first amplifier adopted extremely low noise voltage amplifier, to ensure lowresistance noise can be collected. Its great frequency response makes sure lowfrequency noise do not aberrant. The second amplifier has a great magnifyingcoefficient, which ensures noise can be collected accurately. Two amplifiers in seriesmakes sure the total background noise equals to the first amplifier’s background noise,which weakened the interference of background noise effectively.2. Discussed the relationship between noise and electromigration dominantdefect-grain boundary, confirmed grain boundary noise becomes the dominant noisealong with electromigration process. Grain boundary was equivalent to a two-dimensionscattering flat, combined with free volume conception, a grain boundary free volumenoise model was established. Based on the model, electromigration noise is mainlydetermined by free volume scatter section area S (v f), grain boundary width, freevolume expansion per unit area of grain boundary V/Aetc.. Referring to theelectron wind enhancement factor, grain boundary noise enhancement factor wasproposed, the calculation showed the enhancement of noise at grain boundary reaches to4orders, comparing the1~2orders enhancement of electron wind force, theenhancement of noise at grain boundary is more remarkable.3. Based on the new electromigration noise testing system, designedelectromigration aging experiment and executed noise testing. The results showed noiseamplitude increases periodically at electromigration prophase, once void nucleationoccurs, it increases sharply, with void growth, noise shows aberrance at low-frequencyband. Frequency exponent increases slowly(or increases periodically) within the range0.8-1.5before void nucleation, once void nucleation, it breaks1.5. Besides, frequencyspectrum parameters are also sensitive to exterior stress (temperature,currentdensity)change.4. Verified electromigration noise is fractal signal, fractal dimension candistinguish every phase during electromigration process, reflect the change of defecttypes and noise generation mechanism. Through Bouligand dimension and percolationtheory, noise time series fractal dimension and grain boundary fractal dimension werebonded, through noise dimension token, grain boundary appearance change duringelectromigration can be obtained. Correlation dimension was adopted to characterizethe stochastic or determinate of electromigration noise, the results showed the noisechanged from stochastic signal to chaotic dynamic signal during electromigrationprocess, indicated the noise generation mechanism changes from stochastic dispersion to ballistic chaotic cavity transport. Furthermore, by judging the convergent ofcorrelation dimension, electromigration failure can be predicted.5. Entropy plays an important role in characterizing system irregular or disorderdegree. Multiscale entropy was adopted to analyze electromigration noise complexity.The result showed: at the early stage, electromigration noise is more irregular, noisecomplexity is greater; as void nucleation occurs, electromigration noise becomes moreregular, the complexity decreases obviously. Through the relationship between noisemultiscale entropy and system thermodynamics entropy, It reflects that the disorderdegree of electromigration system decreases continually.