T process step in modern device fabrication, especially for

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1 218 EEE TRANSACTONS ON ELECTRON DkVCPS VOL 38 NO 2 FFBRUARY 991 Low-Temperature Annealing of ArsenidPhosphoms Junctions Mark E. Law, Member, EEE, and James R. Pfiester, Senior Member, EEE Abstract-The formation of arsenic and phosphorus junctions is an important process step in modern device fabrication. The accurate prediction of the vertical and lateral profile is crucial for optimization of the device behavior and reliability. Experimental data show that the damage from implantation of the dopant species has an important and controlling effect on the final profile during low-temperature annealing. Modeling of the dopant and point defect interaction during this anneal indicates that the junction is determined by the number of point defects created during the implantation. This model is compared to experimental data and good agreement is shown for both one- and twodimensional results.. NTRODUCTON HE codiffusion of arsenic and phosphorus is an important T process step in modern device fabrication, especially for lightly doped drain and double-diffused drain MOSFET devices. Because the short-channel MOSFET characteristics are improved with shallow source and drain junctions, the tendency has been to reduce the time and temperature after implantation to form the shallow junctions. With short-time annealing steps, the enhancement in dopant diffusion due to transient effects becomes more pronounced. t is important, therefore, that these transient effects be understood and accurately modeled. Several investigators [ 11, [2] have discussed the enhancement of boron during short-time annealing and have attributed this effect to residual damage from the implantation step. Miyake [3] proposed a model for enhanced boron annealing based on an exponentially decaying enhancement to the diffusivity where D is the total diffusivity, Ddam is the damage-enhanced diffusivity, T is the decay time of the enhancement, which is on the order of a few seconds at 900 C, and D* is the equilibrium diffusivity of the dopant in question. Similarly, Fair 141 proposed an empirical model for annealing of boron at low temperatures which included the effect of implantation damage. This was implemented in the PREDCT [4] program which was compared to experimental data. The model assumes a constant enhancement for a short time which then reverts to the equilibrium diffisivity, as given by D = Ddam, for t < rl, D = D*, fort > ro. (2) Manuscript received January 26, 1990; revised August 20, The review of this paper was arranged by Associate Editor S. E. Laux. M. E. Law is with the ntegrated Electronics Center, Department of Electrical Engineering, University of Florida, Gainesville, FL J. R. Pfiester is with the Advanced Products Research and Development Laboratory, Motorola nc., Austin, TX EEE Log Number The time constant T,, is on the order of several seconds. Good correlation between the extracted times of the Fair model with the transient decay length of Miyake was obtained. The damage-enhanced diffusivity was typically a factor of 25 greater than equilibrium diffusivity. Fair also included the effect of the amount of damage on the amount of enhancement. Although these models are predictive for one-dimensional simulation, they are empirically based and, hence, difficult to extend to multiple dimensions. The only extension is an isotropic enhancement term, but it is unclear whether this is physical. OED exhibits a much faster lateral reduction than vertical, especially for heavily doped structures [5]. Therefore, considerable experimental work must be performed before the isotropic extension can be considered valid. n this paper, a model for damage enhancement is proposed that is suitable for twodimensional simulation. Calibration is performed by using onedimensional experimental work on both boron and arsenic/ phosphorus junctions. Two-dimensional calculations are performed and compared to experimental device data. 11. MODEL FOR DAMAGE ENHANCEMENT mpurity diffusion in silicon occurs through interaction of impurities with point defects, vacancies, and interstitials. To correctly predict the diffusion of impurities, it is necessary to calculate the point-defect concentrations. The properties of the point defects, therefore, are important to understanding any diffusion phenomena. Mathiot and Pfister (61 derived the equations for defects and impurities by assuming that impurities diffuse only through interaction with point defects. The equations below are for a single-donor impurity; assuming that the donor diffuses only when paired with a defect. (3) C refers to the concentration of the subscripted species, J is the flux, and K,. is the bulk recombination constant. The subscripts A,, V, A, AV refer to the donors, interstitials, vacancies, interstitial-donor pairs, and vacancy-donor pairs. The superscript * refers to the equilibrium concentration of the defect, which is a function of the Fermi level and temperature. The defect concentrations are the total concentration of defects including all charge states that are present. This also applies for the defect-donor pairs. Equations (3)-(3, therefore, are valid %01.00 U 1991 EEE

2 ~ LAW AND PFESTER: LOW-TEMPERATURE ANNEALNG OF ARSENCPHOSPHORUS JUNCTONS 219 for any charge states that may exist for either the pairs or the defects. This general expression describes the flux of a given donor impurity provided several assumptions hold. The first assumption is that the donor impurity diffuses only when it is associated with a defect. The second assumption is that the pairs and individual species are in local equilibrium with each other. The last assumption requires that the chemical reactions forming pairs is fast compared to the other processes, and that transients in the formation of these pairs can be neglected. t is difficult to establish the accuracy of the latter assumption except by comparison to large annealing time experiments to determine if the transient is required. Mulvaney [7] has recently performed calculations that assume that the local equilibrium between pairs does not hold. Although this approach does not have to make any assumptions in the derivation of the equations, it does have two drawbacks. 'The first drawback is the necessity of estimating the reaction rates, both forward and reverse, for the chemical reactions involved in the system between the dopants and pairs. For a donor atom that diffuses via a vacancy mechanism in three different charge states, there are a minimum of six different reaction rates to be estimated. The second drawback is that separate differential equations must be solved for each species. n the above example, seven different partial differential equations must be solved numerically. Although tractable in one dimension, the extension to two dimensions would require extensive CPU calculation time. The Mulvaney model will reduce to the model of local equilibrium when the rate constants are very fast. t is interesting, therefore, to see how far the assumption of local equilibrium can be extended in modeling modern technology. The fluxes in (3)-(5) can be treated by analyzing the components of the flux in the different defect charge states. Giles [8] has recently treated the fluxes in a system of equations similar to these. Although previous researchers have included the effect of the field on the charge states of the dopant defect pairs, the effect of the electric field on the defects has been neglected. Both Giles [8] and Law [9] have demonstrated that it is important to include the effect of field on the charged defects. The interstitial donor pair flux JAl can be derived as follows: ni + log - + log - n This can be further simplified since the log n/n, terms cancel and K, is independent of space [lo]. n fact, all pair fluxes can be reduced in a similar fashion. The total pair flux can then be written as -JA = c D,cCApV log CAO. (12) c The term in the summation can be associated with the diffusivity of the dopant interstitial pairs and is dependent on the concentration of pairs and the Fermi level. Giles has modeled the total pair flux in relation to the fundamental variables CA and C, [8]. By computing the balance of the various reactions, he was able to derive complex formulas for the concentration of the pairs. f the assumption that the electronic charging processes are faster than any other reaction is made first, than all possible reactions can be simplified in formation of the pairs. For example, in forming a neutral donor interstitial pair, the most likely reaction would involve a positive donor and negative interstitial. Because electronic charging is assumed instantaneous, the negative interstitial concentration can be simplified using the neutral interstitial concentration and the electron concentration. The total number of pairs can then be written where K is a function only of temperature. This allows substitution into (12) to simplify the flux of the pairs. n addition, the temperature-dependent constants are combined and the diffusivity is referenced to the diffusivity found when the interstitials are at equilibrium where A' refers to the donor interstitial pairs in the c charge state, D is the diffusivity, and the summation is over all the charge states of the donor interstitial pairs. The summation can be simplified if several assumptions about the reactions are made. f the electric processes are assumed to be the fastest, then each charge state concentration can be written in terms of the neutral pair concentration CA+ = K+ nl CA,,, (7) n CA,- = K- CAp ni The flux equation (6) can be further simplified by using the pair relationships in (7) and (8). f we rewrite (6) This diffusion equation for donors is similar to those that have been used in many process simulation programs [ 111, [ 121. One difference, however, is the inclusion of the gradient of the interstitial concentration. Although neglecting this term is suitable for modeling of oxidation injection of interstitials, it is not accurate for the modeling of damage effects on dopant diffusivity. n the case of damage, the defect concentrations will be varying rapidly over several orders of magnitude. The vacancy-impurity fluxes JAv, vacancy flux Jv, and the interstitial flux J, can be derived in a similar fashion. Again, it is important to remember the charge states of the defects for performing this derivation. For example, only the final result for the interstitial flux is given The neutral pair flux can then be written

3 * 280 EEE TRANSACTONS ON ELECTRON DEVCES. VOL. 38, NO. 2. FEBRUARY 1991 The vacancy flux can be written in a similar fashion as grow 225 A oxide C Jv = DvCCV 2. 0 LV KeVP 5-10 BOKeVAs No Anneal 30m 900 C This model can be applied in a straightforward fashion to predict damage enhancement if the concentration of defects created during the implantation is known and the sources and sinks for defects during diffusion are understood and well modeled. The approach taken in this work is to treat the damage created by the implantation as an initial condition of point defects. Although the parameters for the defect equations can be extracted from various gettering [ 131, [ 141 and oxidation [ 151, [16] studies, it is difficult to determine the parameters without examining all the experimental evidence. The parameters for the defects used in this study were extracted from experimental data and included interstitial traps [15], a finite bulk recombination [17], surface effects on both types of defects [17], [18], and defect charge states [8], [19]. n modeling implantation damage effects, it is necessary to estimate the number of defects created from an implant. Hobler and Selberherr [20], using Monte Carlo techniques, estimated the amount of damage from an implant and characterized it using Gaussian profiles, in which the damage is proportional to the dose of the implant. Since this technique does not consider any annealing of defects during the implantation itself, the total damage profile is overestimated. All of the implant-created damage is assumed to be stable-point defects as opposed to extended defects created during implantation, which can be sinks and sources of point defects. Extended defects, including endof-range dislocation loops, are not included in the calculations. End-of-range dislocations will be present [21] under the types of annealing performed in these experiments, but the effect of these is assumed to be small in the simulations and modeling ONE-DMENSONAL EXPERMENTS Kim [22] investigated the effect of implantation damage on one-dimensional structures using high-dose arsenic and phosphorus implants. These implants were annealed for varying lengths of time and very little difference in the dopant profile was noticed as a function of time. Kim attributed this to a shorttime enhancement of the diffusion due to annealing of the damage created during the implantation step. These experiments suggest that lightly doped drain structures will also be influenced by implantation damage. To investigate the effect of damage on the formation of these structures, an experiment [23] was designed to utilize implants and conditions found in normal device fabrication. By reversing the order of the heavy and lightly doped implantation steps, the effect of the damage created by the dopant implants was studied. The experimental flow chart is described in Fig. 1. The two main splits in the experiment include arsenic nf implantation both before and after the phosphorus n- implantation. All the thermal anneals were performed at 900 C in a nitrogen ambient. The anneals were set up such that the phosphorus layer received three different anneal times in each of the main splits. Since the phosphorus n- junction depth is typically deeper than the arsenic nt junction in a lightly doped drain structure, this allows comparison of junction depths to be made between main splits. The right side (wafers 4, 5, and 6) of the flow chart has experiments in which the arsenic is implanted first to form the heavily doped layer. This layer is given a short anneal time of m 900 C No Anneal 30m 900T 60m 900T Fig. 1. Flow chart of the process schedule for the experimental stmctures. Labeled arrows indicate specific splits referred to in the text. 10 min at 900 C which should anneal the point defects created by the implantation. End-of-range dislocations are not removed by this annealing step [21]. The phosphorus implant for the lightly doped layer is then done followed by a split of three different anneal times. A final anneal of 30 min at 900 C completes the sequence. Because the arsenic nf implant is implanted first and followed by a thermal anneal prior to the phosphorus n- implantation, there should be little enhancement of the phosphorus diffusivity. Parrillo [24] has demonstrated an LDD device formed by reversing the implantation order of the AND SMULATONS ni and n- layers which demonstrates reduced phosphorus n- source/drain lateral diffusion. Fig. 2 shows the spreading resistance measurement of wafers 4, 5, and 6, which have the arsenic n+ implant prior to the phosphorus n- implantation for various thermal anneal times. Also shown are simulations based on default diffusivities in which the defect concentrations depend only on the local Fermi level. As shown in Fig. 2, the phosphorus diffusivity must be enhanced compared to default values whereas the arsenic diffusivity is approximately correct. Also the data show no time dependence in the profiles despite the varying thermal anneal times. This indicates that the enhancement does not depend strongly on the thermal anneal time and, therefore, must occur over a short period of time. This type of enhancement is consistent with a damage effect, which would result in an extremely short-time enhancement to the diffusivity of the dopant. f this enhancement is large, the remaining anneal time will do little to change the shape of the final profile. The left side of the flow chart (wafers 1, 2, and 3) receive the lightly doped phosphorus n- implant prior to the arsenic n+ implantation. The wafers are then split again and given three different heat treatments. The high-dose arsenic nt implant follows which creates a large amount of damage in the substrate. A final anneal finishes the sequence. f the damage from the arsenic layer creates a significant enhancement in diffusion, the phosphorus will form a deeper junction. The implant sequence in this split is the conventional order for forming LDD MOS- FET's. n contrast to the other split involving wafers 4, 5, and

4 1 ~ Wafer LAW AND PFESTER: LOW-TEMPERATURE ANNEALNG OF ARSENCPHOSPHORUS JUNCTONS 28 1 N+ before N 4-30m 900 C Wafer 5-60m 900 C % Wafer 6-90m 900 C Default Model Since implantation creates both vacancies and interstitials in equal numbers, the effect of bulk recombination on the defects grows as the square of the amount of damage. Assuming the primary component in the interstitial equation is the bulk recombination and the interstitial and vacancy concentrations are equal Depth in um Fig. 2. Result of spreading resistance on wafers 4, 5, and 6, as well as default diffusivity simulations. Wafers 4, 5, and 6 had the arsenic n' layer implanted before the n- phosphorus layer. m ' N Before N+ Wafer 1 30m 900 C 6 **q% Wafer 2 60m 900 C - m c W - g z m Wafer 3 90m 900 C Default Model Depth in gm Fig 3. Result of spreading resistance on water\ 1, 2, and 3, as well a\ default diffusivity simulations Waters, 2, and 3 had the phosphorus n layer implanted before the ni arsenic layer 6, the phosphorus should diffuse much deeper due to the enhancement from the arsenic implantation damage. Fig. 3 shows the spreading resistance profile for wafers, 2, and 3, which have the phosphorus n- implant prior to the arsenic n+ implantation. The simulations based on default diffusivity values are also shown. Although there is an apparent phosphorus-diffusivity enhancement, these wafers show a dependence on the processing sequence. Wafer l, which does not receive an anneal before the arsenic is implanted, shows less enhancement than do wafers 2 and 3. Wafer 1 receives the phosphorus implant, the arsenic implant, and then the final 30-min anneal. This wafer experiences only one anneal following an implantation. Wafers 2 and 3 receive anneals following both implant steps, and experience enhanced diffusion during both temperature cycles, which result in deeper junctions compares to wafer. There are two important observations to notice in the spreading resistance meausrements. First, the profiles are much deeper than predicted by the accepted diffusivity values. n a pointdefect-based model, there must be a substantial excess of defects to enhance the diffusivity enough to form the deeper junction. Second, the profiles show little dependence on the anneal time. This means that the enhancement to the diffusivity has to have a lifetime much shorter than the shortest anneal time. Most of the diffusion occurs in a short period after the anneal begins. A damage-enhancement model is consistent with these observations since the damage created from the implant can be a sizable fraction of the lattice density. This provides a huge excess of defects to enhance diffusion, which will diffuse and recombine quickly which reduces both the temporal extent of the enhancement and the magnitude of the time-averaged value. ac, G -K,C?. at The solution to this equation has the form 1 c, K,t + l/c,(o)' An estimate for K, may be obtained from ORD data [17] at 1100 C with a value of 2.6 x cm6/s. f C,(t = 0) is lo2' ~ m - the ~, number of defects will have decreased an order of magnitude in 45 ps at 1100 C. This simple estimate indicates that the implantation damage effect is a very-short-term enhancement to the diffusivity. The experimental result indicates that the diffusion in these structures cannot be modeled using classical diffusion modeling techniques. To model the diffusion of these structures, it is necessary to use (3)-(3, and the parameters derived from OED experiments for the defect fluxes and recombination. This allows the model to be self-consistent with calculations of OED in one and two dimensions. The damage from the implant is assumed to create point defects which provides an initial condition for the anneal step. Fig. 4 shows the spreading resistance measurements and the simulations of wafers 4, 5, and 6, which have the n+ implantation before the phosphorus n- implantation. The simulations were performed with the full defect model as described in Section 11. The damage created by the implants is calculated and assumed to be completely mobile and available to enhance diffusion. This approach works well as shown by the good agreement in Fig. 4. Fig. 4 also shows that the simulated profiles have little variation in the time dependence and the enhancement is short term in nature. Fig. 5 shows the results and simulations of wafers 1, 2, and 3, which have the n- phosphorus implantation first. There is a considerable difference in the final junctions of the wafer that received one damage anneal (wafers 1, 4, 5, and 6) and those that receive two (wafers 2 and 3). SUPREM-V simulations support the conclusion that the damage created by both the phosphorus and arsenic implants is important in determining the final implant. The phosphorus implantation step disturbs approximately 10% of the silicon lattice atoms. Assuming the damage forms stable point defects, which is done in these simulations, the enhancement can therefore be very large. SU- PREM-V simulations indicate that the number of times damage is produced and annealed determines the final junction depth. Wafers, 4, 5, and 6 receive one anneal of a damaged layer and show less diffusion than wafers 2 and 3 which receive two damage anneals. This could also be explained through interaction with extended defects [22]. n this case, wafers 2 and 3 would diffuse further since the phosphorus is annealed before the implantation of arsenic. This anneal would produce an enhanced phosphorus diffusion since the phosphorus would not be screened by the extended defects produced in the arsenic implant. The other four wafers could be accounted for by channeling tails of the phosphorus. From this experiment, it is impossible to tell what ex-

5 282 EEE TRANSACTONS ON ELb.CTRON DEVCES. VOL. 38. NO. 2. FEBRUARY 1991 io! E j i t S' Before S k \\ afrr 1-30m C \\aferi60m911oc \yafert-90mgm Siii Defer: ilodel Standard NMOS Process Flow.: id: 2 lfl'i 0 0i U! 03 ll "i nepihln m Fig. 4. Result of spreading resistance on wafers 4, 5, and 6, as well as the damage-enhanced diffusivity simulations. Wafers 4, 5, and 6 had the arsenic n+ layer implanted before the n- phosphorus layer KeV P A 15m 900T Fig. 6. Experimental Row chart for the experimental graded source and drain devices Depth in pn Fig. 5. Result of spreading resistance on wafers 1, 2, and 3, as well as the damage-enhanced diffusivity simulations. Wafers 1, 2, and 3 had the phosphorus n- layer implanted before the n+ arsenic layer. planation is more accurate, as these simulations show good agreement with experiment without including the effect of extended defects. More work is necessary to understand the effect of extended defects and their interaction with point defects. v. TWO-DMENSONAL EXPERMENTS AND SMULATONS The model for damage enhancement can be extended to two dimensions in a straightforward way since the basic model equations are valid in two dimensions. The main problem, however, is an extension of the one-dimensional damage profile into two dimensions. The one-dimensional calculations of Hobler and Selberherr [20] can be extended into two dimensions using the approach of Furakawa [25]. This, in principle, allows calculations of the MOSFET source and drain regions. Verification of the two-dimensional profiles, however, remains difficult as compared to the one-dimensional profile. Several double-drain-diffused drain MOSFET structures were fabricated to investigate the extent of the lateral enhancement of the source and drain junctions. The devices were fabricated similarly until the source and drain implant step. At this step, three experimental splits were made. The experimental flow chart is shown in Fig. 6. The first experimental split had the phorphorus n- implantation first, followed by the arsenic n+ implant. The second split reversed the order of the implants. The final split performed a low-temperature anneal between the arsenic and phosphorus implants. The results from the onedimensional experiments indicate that there should be little difference in the enhancement in these devices since the phospho- rus profiles receive only one anneal of a damaged layer. f channeling is an important effect, then splits 1 and 2 should have a large final difference in junction depth, since the arsenic implant in split 2 will amorphize the substrate and eliminate channeling. This should be sufficient to anneal most of the arsenic damage. Measurements of the electric channel length are a good indication of the amount of diffusion under the gate. f there is a substantial difference in the lateral diffusion, there should be a difference in the electrical channel length measurements. Channel length measurements indicate that all three experimental splits have no significant difference in the lateral diffusion. SU- PREM-V simulations shown in Fig. 7 agree with this result, and the three experiments show little final junction depth variation, in either the vertical or lateral direction. Parrillo [24] described an LDD disposable spacer (DSP) technology which takes advantage of reducing the damage layer effects described in the one-dimensional experiments. n these structures, it is possible to implant the arsenic n- first and then the phosphorus n- layer, while still offsetting the n+ from the gate edge. This implant order is reversed compared to the normal order for lightly doped drain structures. The devices also included a salicided source and drain junction. Since salicidation effects on diffusion are not well understood, it is difficult to simulate these structures directly. A simulation study of the disposable spacer process without salicided junctions can be compared to a normal LDD process. From the one-dimensional experiments, it is expected that the disposable spacer process would produce less lateral diffusion since the phosphorus anneal experiences only a single anneal of a damaged layer. The LDD process implants the phosphorus first and therefore the phosphorus receives two separate anneals. The DSP process implants the phosphorus after the arsenic and anneals the lightly doped layer once. Simulations of these structures were performed using SUPREM-V. Fig. 8 shows the final junction depths of the structures. The LDD process exhibits more vertical and lateral diffusion of the phosphorus n- layer. The LDD vertical junction is 300 A deeper than the junction for the disposable spacer process. Tbe LDD device also has a longer lateral junction by about 300 A. The disposable spacer technology, therefore, seems to offer considerable improvement in the amount of lateral encroachment of the

6 LAW AND PFESTER: LOW-TEMPERATURE ANNEALNG OF ARSENCPHOSPHORUS JUNCTONS, 283 implant ordering using a disposable spacer appears to be an attractive alternative for manufacturing shallow junctions. ACKNOWLEDGMENT The authors would like to thank C. Rafferty, P. Griffin, R, W. Dutton, and J. Alvis for helpful discussions. REFERENCES 1 1,,,, 1, d 0a d.22 a.46 A.62 a.s3 x 1 mlcr-c * Fig. 7. Simulated junction depth for the graded source and drain devices. There is little difference between the process steps, in agreement with experiment 1.E,E d 1; SUPREM-.V A.8930 ill0 Frocess d d a.sa Y m,crcns Fig. 8. Simulated junction depths for a lightly doped drain (LDD) and disposable spacer (DSP) process. The DSP process has less vertical and lateral diffusion than the equivalent LDD process. source and drain junctions which does improve device performance. V. CONCLUSONS n conclusion, experiments and simulations have been performed which indicate three important effects of implantation damage on arseniclphosphorus codiffusion. First, the profiles are primarily determined by the damage-induced injection of defects. Second, damage enhancement is almost independent of anneal time. Third, the effect of the damage from the phosphorus implant is as important as the arsenic implant damage. The modeling of these effects therefore becomes critical for accurate LDD device design. Simulations and experiments on twodimensional device structures indicate that this same phenomena occur laterally under the gate. Reversing the normal LDD [l] S. Guimaraes, E. Landi, and S. Solmi, Enhanced diffusion phenomena during rapid thermal annealing of preamorphized boron implanted silicon, Phys. Status Solidi (a), vol. 95, p. 589, [2) J. F. Marchiando and J. Albers, Effects of ion-implanted damage on two-dimensional boron diffusion in silicon, J. Appl. Phys., vol. 61, no. 4, p. 1380, [3] M. Miyake and S. Aoyama, J. Appl. Phys., vol. 61, p. 1754, [4] R. B. Fair, Low-thermal-budget process modeling with the PREDCT computer program, EEE Trans. Electron Devices, vol. 35, no. 3, p. 285, [5] A. M. Lin, R. W. Dutton, and D. A. Antoniadis, The lateral effect of oxidation on boron diffusion in ( 100 ) silicon, Appl. Phys. Lett., vol. 35, no. 10, p. 799, [6] D. Mathiot and J. C. Pfister, Dopant diffusion in silicon: A consistent view involving nonequilibrium defects, J. Appl. Phys., vol. 55, no. 10, p. 3518, [7) B. J. Mulvaney, W. B. Richardson, and T. L. Crandle, PEP- PER-A process simulator for VLS, EEE Trans. Computer- Aided Des., vol. 8, no. 4, p. 336, [8] M. D. Giles, Defect coupled diffusion at high concentrations, EEE Trans. Computer-Aided Des., vol. 8, no. 4, p. 460, [9] M. E. Law, Two dimensional numerical simulation of dopant diffusion in silicon, Ph.D. dissertation, Stanford University, Stanford, CA, [lo] J. Tsai, J. Appl. Phys., vol. 51, p. 3230, [l 11 C. P. Ho, J. D. Plummer, S. E. Hansen, and R. W. Dutton, VLS process modeling-suprem 111, EEE Trans. Electron Devices, vol. ED-30, no. 11, pp , [12] P. Pichler, W. Jungling, S. Selberherr, E. Guerrero, and H. Potzl, Simulation of critical C fabrication steps, EEE Trans. Computer-Aided Des., vol. CAD-4, no. 4, p. 384, [13] G. B. Bronner and J. D. Plummer, Gettering of gold in silicon: A tool for understanding the properties of silicon interstitials, J. Appl. Phys., vol. 61, no. 12, p. 5286, [14] T. Y. Tan and U. Gosele, Point defects, diffusion processes, and swirl defect formation in silicon, J. Appl. Phys., vol. 37, no. 1, p. 1, [15] P. B. Griffin and J. D. Plummer, Process physics determining 2-D impurity profiles in VLS devices, in EDM Dig. Tech. Pupers (Los Angeles, CA, 1986), p [16] S. T. Ahn, P. B. Griffin, J. D. Shott, J. D. Plummer, and W. A. Tiller, A study of silicon interstitial kinetics using silicon membranes-application to 2-D dopant diffusion, J. Appl. Phys., vol. 62, no. 12, p. 4745, [17] E. Guerrero, W. Jungling, H. Potzl, U. Gosele, L. Mader, M. Grasserbauer, and G. Stingeder, Determination of the retarded diffusion of antimony by SMS measurements and numerical simulations, J. Electrochem. Soc., p. 2182, [18] S. M. Hu, Kinetics of interstitial supersaturation and enhanced diffusion in short-time/low-temperature oxidation of silicon, J. Appl. Phys., vol. 57, p. 4527, [19] G. D. Watkins, EPR studies of the lattice vacancy and low temperature damage processes in silicon, in Lattice Defects in Semiconductors 1974, Huntley, Ed. (1975, nst. Phys. Conf. Ser. 23, London, UK). [20] G. Hobler and S. Selberherr, Two-dimensional modeling of ion implantation induced point defects, EEE Trans. Computer- Aided Des., vol. 7, no. 2, p. 174, [21] K. S. Jones, S. Prussin, and E. R. Weber, A systematic analysis of defects in ion implanted silicon, Appl. Phys. A, vol. 45, no. 1, p. 1-34, [22) Y. Kim, H. Z. Massoud, and R. B. Fair, The effect of ion implantation damage on dopant diffusion in silicon during shallow

7 2 84 EEE TRANSACTONS ON ELECTRON DEVCES. VOL 38. NO. 2. FEBRUARY 1991 junction formation, J. Elecrron. Mar., vol. 18, no. 2, p. 143, M. E. Law, J. R. Pfiester, and R. W. Dutton, The effect of implantation damage on arsenic/phosphorus codiffusion, presented at EDM, San Francisco, CA, L. C. Parillo, J. R. Pfiester, J. H. Lin, E. 0. Travis, R. D. Savin and C. D. Gunderson, Disposable polysilicon LDD spacer technologv. EEE Trans. Electron Devices. vol. 38. no. 1. DD. 39- A 46, fin ~ 5 S. 1 Furakawa, H. Matsumura, and H. shiwara. Japan. J. Appl. Phys., vol. 11, p. 134, * Mark E. Law (S 79-M Sl-S Sl-M 82) received the B.S. degree in computer engineering from owa State University, Ames, in 1981 and the M.S. and Ph.D. degrees in electrical engineering from Stanford University, Stanford, CA, in 1982 and 1988, respectively. His Ph.D. dissertation concerned the two-dimensional numerical modeling of point defect and dopant diffusion in silicon. During this time, he coauthored the SUPREM-V process modeling program. He worked for Hewlett Packard on device and process modeling during 1982 and n 1988, he was a Research Associate in the Department of Electrical Engineering at Stanford University. He joined the faculty of the University of Florida in Gainesville as an Assistant Professor in He won BM Young Faculty Development Award in His research is currently focused on three main areas: bipolar device simulation and modeling; silicon process modeling, with emphasis on the physics of diffusion; and simulation of integrated circuit manufacturing. Dr. Law is a member of Tau Beta Pi, Eta Kappa Nu, and Sigma Xi. * James R. Pfiester (S 75-M 77-S 80-M 84- SM 90) was born in San Diego, CA, on February 12, He received the B.S. degree in electrical engineering, summa cum laude, in 1976 and the M.S. degree in 1977, both from the University of llinois, Urbana-Champaign. He received the Ph.D. degree in electrical engineering from Stanford University, Stanford, CA, in His dissertation investigated the performance limits of CMOS VLS. From 1978 to 1980, he was employed by Motorola, nc. Austin, TX, as a Circuit Designer on the MC b microprocessor chip. From 1981 to 1983, he was a Device Physics Consultant for Hewlett-Packard Corp. From 1984 to 1985, he was a Research Staff Member at the BM Thomas J. Watson Research Center, Yorktown Heights, NY, and was involved in the design of submicrometer CMOS devices. He is currently a Member of the Technical Staff at the Motorola Advanced Products Research and Development Laboratory, Austin, TX, and is involved in the development of advanced CMOS technologies. Dr. Pfiester is a member of the Electrochemical Society, Phi Kappa Phi, the National Society of Professional Engineers, and is a Registered Professional Engineer in the State of Texas.