Application of titanium silicide as an interconnect in deep submicron integrated chip manufacturing 2

Study of Titanium Silicide Formation using Spike Anneal Chapter Study of Titanium Silicide Formation using Spike Anneals 5.1 Introduction To extend the usefulness of TiSi2, integrated chip manufacturers employ either a pre-amorphizing implant (PAI) or an implant through metal (ITM) [5-8] technique to enhance the formation of the desired C54-TiSi2 phase. However, both introduce damage to the substrate, resulting in device degradation like junction leakage and device driving current loss [9-11]. Recently, refractory metals like Mo have been implanted in minute quantities into the Ti film [50]. These act as nucleation sites, which results in smaller C49-TiSi2 grains. However, introducing a new metal species into the IC manufacturing line may not always be desirable. The effect of possible contamination to the existing process from the new metal species is unknown. Although TiSi2 can be replaced by alternative metal silicides namely, Co or Ni as both metal silicides are proven at deep sub-micrometer [51], the change in silicide technology can be costly. In this chapter, an alternative option designed to extend the usefulness of TiSi2 is presented. Spike anneals are studied in three areas, namely, different spike temperatures with a fixed soak time at a lower temperature, a fixed spike temperature with different soak times at a lower temperature, and different spike temperatures without any soak time. Page 69 Study of Titanium Silicide Formation using Spike Anneal 5.2 Experimental Procedure Experiments were performed on 8” (200mm) wafers from 0.35 µm CMOS logic technology. A 450/150 Å Ti/TiN stack is first deposited using PVD on patterned poly Si lines with SiO2 spacers. These undoped poly Si lines are on the field SiO2. The deposition was carried out within hours after a brief dip in a dilute HF solution that removed any native SiO2. Ti silicide was then formed in two RTA steps. All RTAs were carried out using an AST-SHS 3000 system with symmetrical double-sided heating on the front and backsides of the wafer. During heating, the wafers spun at approximately 85 rpm in the chamber for better uniformity. For better peak temperature control and repeatability, the heating rate in all the spike anneals was controlled at 125 Ks-1 ramp up, this is well within the maximum possible ramp up rate of 300 Ks-1. Three peak temperatures for the spike anneals were used, namely 800, 850 and 900 °C. Table 5-1 gives the details of the RTA1 conditions used in this study. Specimen A, the control specimen, was prepared using the standard RTA1 recipe, 720°C for 30s. The ramp-up rate for specimen A was 35 Ks-1. Except for specimen A, the soak times during RTA1 were reduced to compensate for the extra thermal budget as a result of an initial spike anneal. It should be noted that the total time above 720°C during each spike was approximately 10 s. Kelvin and Serpentine Comb structures were used to measure the sheet resistance and gate-to-source/drain leakage current for various line widths. For sheet resistance measurements, the line widths were varied from 1.0 to 0.275 µm. Page 70 Study of Titanium Silicide Formation using Spike Anneal Table 5-1. Details of RTA1. Specimen RTA1 detail A 720°C, 30 s soak B Spike at 800°C, 20 s 720 °C soak C Spike at 850°C, 20 s 720 °C soak D Spike at 900°C, 20 s 720 °C soak E Spike at 850°C, 10 s 720 °C soak F Spike at 800 °C G Spike at 850 °C H Spike at 900 °C After RTA1, selective etching of unreacted Ti and TiN (etchback) was carried out using solution SC1 (NH3OH:H2O2:H2O at 1:1:10). The second anneal, termed RTA2, at 850 °C for 30 s converts the silicide formed to the C54-TiSi2 phase. To isolate the effects of spike anneals in these experiments, no PAI or ITM was employed. Transmission Electron Microscopy (TEM) characterizations were performed on specimens G and H to observe the integrity of the Ti silicide on the 0.25 µm serpentine structure. 5.3 Results 5.3.1 Sheet resistance Different spike temperatures with a fixed soak time at a lower temperature Figures 5-1(a) and 5-1(b) respectively show the sheet resistance of specimens A, B, C and D measured after etchback and RTA2. Results from specimen A are Page 71 Study of Titanium Silicide Formation using Spike Anneal shown in Figures 5-1(a) and 5-1(b) for comparison purposes. From Figure 5-1(b), the specimens that experienced a spike during RTA1 registered a lower sheet resistance as compared to specimen A. Specimens with a higher initial spike temperature had lower sheet resistances. The difference in the sheet resistance after RTA2 increases with decreasing line width suggesting that the initial high temperature spike reduces the area-dependence of the C49-to-C54 titanium silicide phase transformation. When in contact with Si surface, the deposited 45nm of Ti likely to be fully consumed during reaction for all specimens. The sheet resistances of the specimen D after etchback and RTA2 not show much difference from Figures 5-1(a) and 5-1(b), indicating that the dominant titanium silicide phase of specimen D after RTA1 is C54. Likewise for specimen C, C54-TiSi2 is the dominant phase after RTA1. As for specimen B, high sheet resistance and high standard deviation shown in Figure 5-1(a) suggests a mixed C49/C54 TiSi2 phase. 16 A: RTA1 720C 30s soak 14 B: RTA1 800C spike, 20s 720C soak 12 C: RTA1 850C spike, 20s 720C soak Sheet Rho (ohm) D: RTA1 900C spike, 20s 720C soak 10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.1 Line Width (µm) Figure 5-1(a) Comparing sheet resistance after etchback for specimens with different spike temperatures plus a fixed soak time at a lower temperature during RTA1. Page 72 Study of Titanium Silicide Formation using Spike Anneal 14 A: RTA1 720C 30s soak 12 B: RTA1 800C spike, 20s 720C soak C: RTA1 850C spike, 20s 720C soak 10 Sheet Rho (ohm) D: RTA1 900C spike, 20s 720C soak 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.1 Line Width (µm) Figure 5-1(b) Comparing sheet resistance after RTA2 for specimens with different spike temperatures plus a fixed soak time at a lower temperature during RTA1. It is interesting to note that the sheet resistance of specimen D remains low even at small linewidths. This indicates that the high temperature spike at 900°C did not result in agglomeration of the thin silicide film. A fixed spike temperature with different soak times at a lower temperature Figures 5-2(a) and 5-2(b) show the sheet resistance after etchback and RTA2 respectively. For RTA1, specimens C, E and G experienced a spike at 850°C followed by a lower temperature anneal at 720°C for 20, 10 and 0s, respectively. It is noted from Figure 5-2(a) that except for specimen A, the formation of the C54-TiSi2 phase in specimens C, E and G after RTA1 is evident. Even when the sheet resistance is somewhat higher at the smaller line widths, it is accompanied by a high standard deviation indicating a mixture of C49/C54 TiSi2 phases. As compared to specimen A Page 73 Study of Titanium Silicide Formation using Spike Anneal in Figure 5-2(a), the sheet resistance remains around 10 ohm indicating a dominance of C49-TiSi2 phase. 16 A: RTA1 720C 30s soak 14 G: RTA1 850C spike 12 E: RTA1 850C spike, 10s 720C soak Sheet Rho (ohm) C: RTA1 850C spike, 20s 720C soak 10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.1 Line Width (µm) Figure 5-2(a). Comparing sheet resistance after etchback for specimens with a fixed spike temperature plus different soak times at a lower temperature during RTA1. 14 A: RTA1 720C 30s soak 12 G: RTA1 850C spike E: RTA1 850C spike, 10s 720C soak 10 Sheet Rho (ohm) C: RTA1 850C spike, 20s 720C soak 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.1 Line Width (µm) Page 74 Study of Titanium Silicide Formation using Spike Anneal Figure 5-2(b). Comparing sheet resistance after the RTA2 treatment for specimens with a fixed spike temperature plus different soak times at a lower temperature during RTA1. From Figure 5-2(b), the increase in the sheet resistance with decreasing line widths for specimen A can be observed, indicating the area-dependency of the C49-toC54 TiSi2 phase transformation. However, the specimens C, E and G show low sheet resistance down to a line width of 3.0 µm. At a line width of 0.275 µm, the specimen C reveals a higher sheet resistance of 4.8 ohm whereas the resistance of both specimens E and G remains low. Moreover, as shown in Figure 5-2(b), the standard deviation for the specimen C at a line width of 0.275 µm is much larger, indicating an incomplete phase transformation. Different spike temperatures without any soak time. Figures 5-3(a) and 5-3(b) show the sheet resistances of the specimens A, F, G and H after etchback and RTA2, respectively. Although the specimens F, G and H did not receive an isothermal soak, the duration at which the temperature of these specimens was above 720 °C was approximately 10 s. Page 75 Study of Titanium Silicide Formation using Spike Anneal 16 A: RTA1 720C 30s soak 14 F: RTA1 800C spike Sheet Rho (ohm) 12 G: RTA1 850C spike H: RTA1 900C spike 10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.1 Line Width (µm) Figure 5-3(a). Comparing sheet resistance after etchback for specimens with different spike temperatures without any soak time during RTA1. 14 A: RTA1 720C 30s soak 12 F: RTA1 800C spike G: RTA1 850C spike Sheet Rho (ohm) 10 H: RTA1 900C spike 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.1 Line Width (µm) Figure 5-3(b). Comparing sheet resistance after RTA2 treatment for specimens with different spike temperatures without any soak time during RTA1. Page 76 Study of Titanium Silicide Formation using Spike Anneal Figures 5-3(a) and 5-3(b) show the sheet resistance of the specimen H to be ohm down to 0.275 µm. Hence, C54-TiSi2 is clearly the dominant phase for the specimen H after etchback and RTA2. For the specimens F and G after etchback, Figure 5-3(a) suggests the presence of a mixed C49/C54 TiSi2 structure. This is evident both from the sheet resistance measurements and also from the high standard deviation. It is interesting to note that the specimen G shows a low sheet resistance for larger line width after etchback (Figure 5-3(a)), suggesting the dominance of C54TiSi2. In Figure 5-3(b) all specimens, except the specimen H, show an area dependency of C49-to-C54 TiSi2 phase transformation. However, the area-dependency effect is somewhat delayed for the specimens F and G compared to the specimen A. At a line width equal to 0.275 µm as shown in Figure 5-3(b), the specimen G has a sheet resistance of 2.37 ohm compared to 3.40 ohm for specimen F and G. This suggests a higher spike temperature is more resistant to the area-dependency of the phase transformation. 5.3.2 Gate-to-source/drain leakage current Measurements were taken on serpentine comb structures with line widths 0.35, 0.33, 0.30, 0.28 and 0.25 µm with a total length of 8400 µm and a 0.7 µm pitch. The applied voltage across gate-to-source/drain was swept from –5 to +5 V. Should there be excessive Si diffusion over the spacers leading to bridging, the profile of the measured current would indicate a resistive (ohmic) connection. Page 77 Study of Titanium Silicide Formation using Spike Anneal Gate to source/drain leakage current for 0.25 µm poly serpertine comb 1.20E-09 A: 35C/s Ks-1 to 720C 30s soak 1.00E-09 8.00E-10 leakage current (A) 6.00E-10 4.00E-10 2.00E-10 -5 -4 -3 -2 0.00E+00 -1 -2.00E-10 -4.00E-10 -6.00E-10 -8.00E-10 -1.00E-09 applied voltage (V) Figure 5-4(a) Gate-to-source/drain leakage current versus applied voltage on a line width equal 0.25 µm taken from specimen A after the RTA2 treatment. Gate to source/drain leakage current for 0.25 µm poly serpertine comb 0.025 D: 900C spike, 20s 720C soak 0.02 leakage current (A) 0.015 0.01 0.005 -5 -4 -3 -2 -1 -0.005 -0.01 -0.015 -0.02 -0.025 applied voltage (V) Page 78 Study of Titanium Silicide Formation using Spike Anneal It was also observed that the sheet resistance after the RTA2 treatment with 0.275 µm poly lines is lower for specimens without any soaking time during the RTA1 treatment. Figures 5-8(a) and 5-8(b) show the sheet resistance taken after etchback and RTA2 respectively for specimens B, C, D, F, G and H. The specimens B, C and D received a 20s 720 °C soak during their RTA1 treatments whereas the specimens F, G and H did not. All the specimens spike annealed at different temperatures, namely, 800, 850 and 900 °C, are compared. From Figure 5-8(b) it can be seen that for a line width of 0.30 µm or above, there is a minimal difference between the specimens with a 20 s soak and those without soak. For example, comparing these line width specimens B and F, although both were spike-annealed at 800 °C during the RTA1 treatment, only specimen B was soaked at 720 °C for 20 s. Figure 5-8(b) shows that the sheet resistance of these line width specimens B and F after the RTA2 treatment not show much difference. However, at a poly line width of 0.275 µm, the sheet resistance of specimen F after the RTA2 treatment is lower than that of specimen B. It is noted that in all cases, the sheet resistances of the specimens without a soak (F, G & H) after the RTA2 treatment is lower at a line width of 0.275 µm. Moreover, the sheet resistance for specimens without a soak after the RTA1 treatment with a line width of 0.275 µm is also lower. This is a specific behavior associated with a poly line width of 0.275 µm. It is believed that the extra thermal budget from the 20 s 720 °C soak might have caused C54-TiSi2 grains to grow at the expense of the existing C49-TiSi2 grains. This would result in an uneven silicide film. Hence, segments of thin C49-TiSi2 phase across the entire narrow poly line width would raise the sheet resistance. This is not observed with larger poly lines possibly because the larger line widths could have accommodated more grains Page 88 Study of Titanium Silicide Formation using Spike Anneal along their breadth and also because the silicide film would be thinner on smaller line widths. 5.5 Summary High temperature spike anneals as a part of the RTA1 treatment delayed the area-dependency of the C49-to-C54 TiSi2 phase transformation. It is believed that the high temperature spike anneal resulted in a higher rate of nucleation and C54-TiSi2 grains during the RTA1 treatment. Although, spike anneals at 900 °C resulted in gateto-source/drain bridging, spikes anneals at 850 °C or lower did not. A one-step RTA salicide is possible for larger line widths incorporating a high temperature spike anneal during the RTA1 treatment. Page 89 Conclusion Chapter Conclusions In summary, C54 phase titanium silicide has successfully been formed on polySi line widths of less than 0.35 µm without the use of pre-amorphizing implants or any other extra steps. This can be achieved by either increasing the ramp-up rate or employing a spike anneal. The use of pre-amorphizing implants to enhance the formation of the C54 phase titanium silicide has been studied in terms of the kinetics of formation. Increasing the ramp-up rate during the first RTA treatment can enhance the the formation of C54-TiSi2 phase without compromising the gate-to-source/drain leakage performance of the IC device. A minimal increase in the ramp-up rate during the RTA1 treatment is needed before its effects are manifest. Results suggest that increasing the temperature ramp-up rate during the first RTA treatment produces smaller C49-TiSi2 grains. A similar TiSi2 sheet resistance can be achieved using a higher ramp-up rate and shorter soak time during the first RTA treatment, as compared to a low ramp-up rate and longer soak time. The formation of TiSi2 by thermal annealing of a single titanium film deposited on silicon substrates with varying degrees of amorphization has been investigated using a differential scanning calorimeter. An exothermic peak corresponding to the formation of the C49-TiSi2 phase has been observed in all cases. The activation energy for the formation of the C49-TiSi2 phase was obtained and found to be in a range of 1.53~2.04 eV. With increasing Si substrate amorphization the activation energy increases initially before it decreases. A second exothermic peak was recorded in the DSC traces when there was a sufficient degree of Si substrate amorphization. This new peak occurs before the formation of the C49-TiSi2 phase and was not due to Page 89 Conclusion recrystallization of the Si substrate. XRD spectra suggest that the new exothermic peak could be due to the formation of Ti5Si3 and Ti5Si4 phases. It is believed that the formation of Ti5Si3 reduces the Gibbs free energy of the system prior to the formation of the C49-TiSi2 phase. This results in an increase in the activation energy for formation of the C49-TiSi2 phase. A higher degree of Si substrate amorphization raises the Gibbs free energy and allows the formation of the Ti5Si4 phase. Although the formation of the Ti5Si4 phase also reduces the Gibbs free energy of the system, the activation free energy barrier for the C49-TiSi2 phase formation is reduced. This suggests that the Gibbs free energy of formation of the Ti5Si4 phase is higher than its reactants in a crystalline form: Ti and Si. This postulate is in agreement with the Gibbs free energy calculations presented here. High temperature spike anneals in the RTA1 treatment have delayed the areadependency of the C49-to-C54 TiSi2 phase transformation. It is believed that the high temperature spike resulted in a higher rate of nucleation and C54-TiSi2 grains during the RTA1 treatment. Although spike anneals at 900 °C resulted in gate-to-source/drain bridging, spikes anneals at 850 °C or lower did not. A one-step RTA salicide treatment is possible for larger line widths with a high temperature spike anneal during the RTA1 treatment. Page 90 Future Recommendation Chapter Future Recommendation 7.1 Introduction Although TiSi2 is fast being replaced by either cobalt or nickel silicide, published papers have reported C54-TiSi2 formation on line widths as small as 60 nm [54] using implanted refractory metals acting primarily as nucleation sites. TiSi2 as an interconnect possesses certain inherent advantages, namely low resistivity, low silicon substrate consumption and good thermal stability. Together with new and better manufacturing tools, it is in the opinion of the author that the usability of TiSi2 can be further extended. Among the many techniques of extending TiSi2 usage, the most researched methods are laser annealing and the implant of refractory metals. However, there exists other novel and possible methods, some of which have been experimented with in a preliminary way during the course of this research but have not been as yet exhaustively researched. These are: spike anneal with PAI/ITM, multi-spike anneal and induction heating. 7.2 Spike Anneal with Pre-Amorphization-Implant/Implant-Through-Metal The results presented in chapter show the advantage of employing spike anneals. In chapter 4, it has been concluded that a Pre-Amorphization-Implant (PAI) increases the substrate strain energy and lowers the activation energy for the formation of the C49-TiSi2. Hence, there is a clear advantage to combine these two techniques. It is in the opinion of the author that with an initial PAI or Implant-Through-Metal (ITM) to lower the activation energy for the formation of the C49-TiSi2, the benefit of a high Page 91 Future Recommendation temperature spike anneal could be better exploited. This might result in a higher driving force for the formation of the C49-TiSi2 phase during annealing. 7.3 Multi-Spike Anneals An idea to form smaller C49-TiSi2 grains involving thermal cycles that would cause nucleation of C49-TiSi2 during each ramp-up cycle slowly evolves to a multispike anneal process. When spike anneals employing ramp-up rates as high as 200 Ks-1 reach the desired temperature, the heating elements would be immediately switched off to allow maximum cooling. Although the furnaces used in RTA processes not have cooling facilities built-in, the wafer would still cool rapidly because RTA furnaces are essentially cold-walled. Some preliminary studies have been conducted. Two silicon wafers were sputtered with 450 Å of titanium followed by 150 Å of titanium nitride. Sample A was spike annealed times to 675 °C at a target ramp rate of 150 Ks-1. Sample B, acting as a control sample, was ramped-up at 35 Ks-1 to 675 °C for 30 s. For this preliminary study, the number of spike-anneals was chosen to be 3. This is because the time needed to perform spike-anneals is roughly the same as that for the control sample. The temperature 675 °C was chosen, as it is high enough to form the C49-TiSi2 phase while not sufficient to transform it to the C54-TiSi2 phase. After removing the capping titanium nitride and any unreacted titanium, planar TEM micrographs (example: figure 7.1) were then taken and the average grain sizes of both samples were approximately determined by the counting the number of grain boundaries cut by an arbitrary line across the micrographs. Table 7.1 shows the measurements taken from the TEM micrographs Page 92 Future Recommendation Sample A Sample B Figure 7-1. TEM micrographs for (a) sample A (3 spike anneals) and (b) sample B (35 °C/s ramp-up with 30s soak) respectively. Table 7-1 measured grain size for spike anneals RTA1 scheme Grain Size (µm) Sample A spikes to 675 °C 0.134 Sample B 35 Ks-1 to 675 °C for 30 s 0.187 The results in Table 7-1 suggest that spike anneals would increase nucleation density as postulated. However, the challenge in multi-spike annealing lies in the repeatability of the spike anneal temperatures. Spike annealing typically employs a ramp-rate around 100 to 200 Ks-1. This high heating rate makes it extremely difficult to control the target temperature during a spike anneal. Page 93 Future Recommendation 7.4 Induction heating The novelty of induction heating to form TiSi2 lies in the fact that it will be a self-limiting process. Here, the titanium film would be heated by Eddy currents induced by a circular coil with an alternating current. Si wafer deposited with Ti film. Induction Induction coils Coilstoto generate Eddy generate Eddy currents currents on the Ti film deposited on the Ti film deposited on on the the Si Si wafer wafer Figure 7-2. Schematic of a silicon wafer deposited with titanium being annealed with induced Eddy currents generated by induction coils. From the setup shown in Figure 7-2, Eddy currents induced by the inductor coils would flow mainly in the titanium film which is of the lowest resistance as compared to the silicon wafer. As the Eddy current heats up (I2R) the titanium film to temperatures around 650 °C, the C49-TiSi2 phase forms. The resistivity of TiSi2 (the C49 phase) is only half that of Ti. Hence the heat from the Eddy current is reduced significantly as the resistance reduces, and thus is a self-limiting process. Furthermore, areas on the silicon wafer with thinner TiSi2 would experience higher heating thereby Page 94 Future Recommendation resulting in a more uniform TiSi2 film as a result. Also, a high temperature ramp-up rate is possible using this technique, as it employs neither conduction nor convention as a means of heat transfer. High ramp-up rates would mean smaller grains and hence enhance the formation of the C54-TiSi2 phase. Below is given a simple approximation of the required magnetic field and current from the coil to heat up 450 Å of titanium deposited on a 200mm diameter mm silicon wafer. Energy requirement: Diameter of Si wafer: 200 x 10-3 m Thickness of Si wafer: 700 x 10-6 m Thickness of Ti deposited: 450 x 10-10 m Density of Si: 2.33 kg/m3 Density of Ti: 4.504 kg/m3 Mass of Si: 2.2 x 10-5 kg Mass of Ti on Si wafer: 2.5 x 10-8 kg Specific Heat of Si: 679 J/kg K-1 Specific Heat of Ti: 528 J/kg K-1 For any reaction to occur, the temperature of the titanium must be 650 °C, and therefore the amount of heat needed is 9.72 J Assuming no heat loss and a 10s ramp up time, the power required is approximately W. Page 95 Future Recommendation Coil current requirment: Resistivity of Ti, ρt ≈ 42 µΩcm Resistance of titanium film = ρt · π · r2 / t = 1.17 Ω Required induced current on titanium film, I’ = 0.92 A Magnetic field for a long straight solenoid, Bs = µo · n · I where µo is the magnetic permeability in air, n the number of coils in the solenoid and I the coil current. Induced magnetic field in a circular disc (radius, r), Bi = ½ · µo · lnr · I’ where I’ is the induced current. Equating Bs and Bi, I = 1/2n · lnr · I’ A preliminary test conducted using a normal 50 Hz household electrical supply manages to heat an inch square (25mm x 25mm) sample taken from a 200 mm silicon wafer with titanium deposited onto it a mere 150 °C. The reason for the low heating efficiency is believed to be the high depth of penetration by the magnetic field and the minute thickness of the sample. Depth of penetration, δ = πfµσ Where f is the frequency, µ is the magnetic permeability, and σ is the electrical conductivity. The magnetic permeability of titanium, µt = 1.005 x µo. Page 96 Future Recommendation Hence, the depth of penetration is 46 mm which is much larger than the thickness of either the titanium film or the entire silicon wafer. The challenge here would be achieving a high frequencies alternating current in order to achieve localized heating in the titanium film. Since the deposited titanium film would be typically in the range of 35 to 60 nm, an extremely high frequency would be necessary to reduce the depth of penetration of the magnetic field. Page 97 Reference Reference [1] S. P. Murarka, JVST. 17, 775 (1980). [2] K. Maex. Mater. Sci. & Eng. R., 11 (2-3), 53-153 (1993) [3] Z. Ma and L. H. Allen. J. Appl. Phys. 77 (9), 4384-4388 (1995). [4] O. Tatsuya, N. Shin-ichi, K. Mitsuo, M. Toyota, N. Akira, U. Yukihiro, Y. Takashi, O. Mizuki, S. Masanobu and I. Hiroshi, “Analysis of Resistance Behavior in Ti- and Ni-Salicide Polysilion Films,” IEEE Trans. on Electron Dev., 41, No. 12, 2305, 1994. [5] K. Fujii, K. Kikuta and T. Kikkawa, 1995 Symp. VLSI Technol. Digest Tech. Papers, 57-58 (1995). [6] J. A. Kittl, D. A. Prinslow, P. P. Apte and M. F. Pas, Appl. Phys. Lett. 67, 2308-2310 (1995). [7] J. A. Kittl, Q. Z. Hong, M. Rodder, D. A. Princlow and G. R. Misium, 1996 Symp. VLSI Technol. Digest Tech. Papers, 14-15 (1996). [8] E. Nagasawa, H. Okabayashi and M. Morimoto, IEEE Transactions on Electron Dev., ED-34 (3), 581-586 (1987). [9] J. Y. Tsai and S. W. C. Yeh, 1997 International Symposium on VLSI Technology, Systems, and Applications, 28-33 (1997) [10] E. H. Lim, S. Y. Siah, C. W. Lim, Y. M. Lee, J. Z. Zheng, R. Sundaresan and K. L. Pey, Proc. of the SPIE – The Int. Soc. for Optical Eng., 3881, 152-158 (1999). Page 98 Reference [11] P. Sallagoity, A. Losavio, T. Marangon, F. Pipia and G. Mastracchio, ESSDERC’99, Proceedings of the 29th European Solid-State Device Research Conference, 644-647 (1999). [12] S. P. Murarka and D. B. Fraser, J. Appl. Phys. 51 (1), 342-349 (1980). [13] L. S. Hung, J. Gyulai, and J. W. Mayer. J. Appl. Phys., 54 (9), 5076-5080 (1983). [14] R. D. Thompson, H. Takai, P. A. Psaras, and K. N. Tu, J. Appl. Phys. 61 (2), 540-544. (1987). [15] L. A. Clevenger, R. W. Mann, R. A. Roy, K. L. Saenger and C. Cabral Jr., J. Appl. Phys. 76 (12), 7874-7881. (1994). [16] E. Ma, L. A. Clevenger, C. V. Thompson and K. N. Tu, Mat. Res. Soc. Symp. Proc., 187. (1990). [17] T. Stark, L. Gutowski, M. Herden, H. Grunleitner, S. Kohler, M. Hundhausen and L. Ley, Microelectronic Eng., 55, 101-107. (2001). [18] T. Ohguro, S. Nakajima, M. Koike, T. Morimoto, A. Nishiyama, Y. Ushiku, T. Yoshitomi, M. Ono, M. Saito, and H. Iwai, IEEE Trans. Electron Dev., 42, 2305 (1994). [19] D. Z. Chi, D. Mangelinck, A. S. Zuruzi, A. S. Wong and S. K. Lahiri, J. Electronic Mater., 30, No. 12, 483-1488 (2001). [20] F. Deng, R. A. Johnson, P. M. Asbeck, S. S. Lau, W. B. Dubbelday, T. Hsiao, and J. Woo, J. Appl. Phy., 81, 8047 (1997). Page 99 Reference [21] R. Mukai, S. Ozawa, and H. Yagi, Thin Solid Films, 270, 567 (1995). [22] R. Ditchfield and E. G. Seebauer. J. Electrochem. Soc., 144, No. 5, (1997). [23] H. E. Kissinger, Analy. Chem., 29, 1702 (1957) [24] S. P. Parker, McGraw-Hill Encyclopaedia of Chemistry, McGraw Hill Inc., N. Y. (1983). [25] B. D. Cullity, “Elements of X-Ray Diffraction 2nd edition”, Addison-Wesley Pub. Co., Boston. (1978). [26] C. C. Tan, L. Lu, S. Y. Chen, Z. X. Shen, A. See, L. H. Chan, L. H. Chua and T. K. L. Chan, J. Vac. Sci. Technol. B, 17(5) 2239 (1999). [27] R. Gregor, C. Ng, J. Libous, E. Carter, R. Beaudoin, A. Chu, D. Grindel, J. Kinney, M. Lee, L. Mentes, J. Oppold, M. Russell, A. Sector, and G. Yenik, IEEE custom Integrated Circ. Conf., 23.1.1-4 (1993). [28] Z. Ma and L. H. Allen, Phys. Rev. B, 49, No. 19, 13 501 (1994). [29] R.J. Nemanich, R. W. Fiordalice, and H. Jeon, IEEE J. Quantum Electron, 25, 997 (1989). [30] J. Hyeongtag, C. A. Sukow, J. W. Honeycutt, G. A. Rozgonyi, and R. J. Nemani, J. Appl. Phys., 71, 4629 (1992). [31] M. F. Ashby and D. R. H. Jones, Chap. & 6. (1994). [32] Lim Eng Hua, private communication. [33] R. Beyers and R. Sinclair, J. Appl. Phys. 57, 5240 (1985). Page 100 Reference [34] R. K. Shukla and, J. S. Multani, 1987 Proc. of the Fourth Int. IEEE VLSI Multilevel Interconnection Conf., 470-479 (1987). [35] C. Y. Ting, F. M. d’Heurle, S. S. Iyer and P. M. Fryer. J. Electrochemical Soc., 133, 2621-2625 (1986). [36] L. A. Clevenger, C. Cabral Jr., R. A. Roy, C. Lavoie, J. Jordan-Sweet, S. Brauer, G. Morales, K. F. Ludwig Jr. and G. B. Stephenson, Thin Solid Films, 289, 220-226 (1996). [37] I. Barin, Thermochemical Data of Pure Substance. Weinheim. VCH. (1993). [38] M. Chase, JANAF Thermochemical Tables, 3d edn, AIP. (1986). [39] J. D. Cox, D. D. Wagman, V. A. Medvedev, CODATA Key Values for Thermodynamics. Hemishpere Publishing Co. (1989). [40] O. Kubaschewski, and C. B. Alcock, Metallurgical Thermochemistry. Pergamon Press. (1979). [41] E. P. Donovan, F. Spaepen, D. Turnbull, J. M. Poate, and D. C. J. Jacobson, J. Appl. Phys., 57, 1975 (1985). [42] P. A. STOLK PA, F. W. SARIS, A. J. M. BERNTSEN, W. F. VANDERWEG, L. T. SEALY, R. C. BARKLIE, G. KROTZ and G. MULLER, J. Appl. Phys., 75 (11) 7266-7286. (1994). [43] W. K. Chu, H. Krautle, J. W. Mayer, H. Muller, M. A. Nicolet and K. N. Tu, Appl. Phys. Lett., 25 (8) 454-457. (1974). [44] S. V. Meschel, O. J. Kleppa, J. Alloys Compds., 267 128-135 (1998). [45] L. Topor, O. J. Kleppa, Metall. Trans. A, (Physical Metallurgy and Material Science), 17A (7), 1217-1221 (1986). Page 101 Reference [46] R. A. Powell, R. Chow, C. Thirdandam, R. T. Fulks, I. A. Blech and J. D. T. Pan, IEEE Electron Dev. Lett., EDL-4, 380-382 (1983). [47] J. T. Pan and I. Blech, J. Appl. Phys., 55, 2874-2880 (1984). [48] N. I. Morimoto, J. W. Swart and H. G. Riella, Appl. Surf. Sci., 38, 48 (1989). [49] J. A. Kittl and Q. Z. Hong, Thin Solid Films, 320, 110-121 (1998). [50] J. A. Kittl, Q. Z. Hong, M. Rodder and T. Breedijk, IEEE Electron Device Lett., 19 (5), 151-153 (1998). [51] A. Lauwers, P. Besser, T. Gutt, A. Satta, M. de Potter, T. Lindsay, N. Roelandts, F. Loosen, S. Jin, H. Bender, M. Stucchi, C. Vrancken, B. Deweerdt and K. Maex, Microelectronic Eng., (50) 103-116 (2000). [52] B. Chenevier, O. Chaix-Pluchery, L. Matko, J. P. Senateur, R. Madar and F. La Via, Appl. Phy. Lett., 79 (14) 2184-2186 (2001). [53] G. V. Samsonov and I. M. Vinitskii, Handbook of Refractory Compounds, Plenum Press, New York (1980). [54] J. A. Kittl, Q. Z. Hong, M. Rodder and T. Breedijk, International Electron Devices Meeting 1997 (IEDM'97), 111- 114 (1997). Page 102 [...]... widths of less than 0.35 µm without the use of pre-amorphizing implants or any other extra steps This can be achieved by either increasing the ramp-up rate or employing a spike anneal The use of pre-amorphizing implants to enhance the formation of the C54 phase titanium silicide has been studied in terms of the kinetics of formation Increasing the ramp-up rate during the first RTA treatment can enhance... C54-TiSi2 formation on line widths as small as 60 nm [54] using implanted refractory metals acting primarily as nucleation sites TiSi2 as an interconnect possesses certain inherent advantages, namely low resistivity, low silicon substrate consumption and good thermal stability Together with new and better manufacturing tools, it is in the opinion of the author that the usability of TiSi2 can be further... in the range of 8.50- 12. 50 ohm, with the smaller linewidths having a higher resistance and the larger linewidths having a lower resistance Given the resistivity of the C49-TiSi2 phase to be 60-90 µΩcm-1 [2] , this result indicates the presence of a dominance of, if not total, C49-TiSi2 phase in specimen A after RTA1 This is not the case for specimens after a spike anneal For specimens with a spike anneal... ramp-up rate and shorter soak time during the first RTA treatment, as compared to a low ramp-up rate and longer soak time The formation of TiSi2 by thermal annealing of a single titanium film deposited on silicon substrates with varying degrees of amorphization has been investigated using a differential scanning calorimeter An exothermic peak corresponding to the formation of the C49-TiSi2 phase has been... C49-TiSi2, which in turn results in smaller C49-TiSi2 grains Smaller C49-TiSi2 grains create more triple grain boundary junctions, which act as nucleation sites for the thin film C49-to-C54 TiSi2 phase transformation Other than increasing the nucleation rate of the C49-TiSi2 phase, the results also suggests other factors arising from the spike anneal which contribute to enhance the C49-to-C54 TiSi2 phase... of titanium silicide after RTA2 treatment Page 87 Study of Titanium Silicide Formation using Spike Anneal It was also observed that the sheet resistance after the RTA2 treatment with 0 .27 5 µm poly lines is lower for specimens without any soaking time during the RTA1 treatment Figures 5-8(a) and 5-8(b) show the sheet resistance taken after etchback and RTA2 respectively for specimens B, C, D, F, G and... resistance results clearly show that a spike anneal in RTA1 reduces the area-dependency of the C49-to-C54 TiSi2 phase transformation The initial effect of having a spike in RTA1 is believed to increase the nucleation rate of the C49-TiSi2 phase This is why the spike anneal was always positioned before the lower temperature soak during RTA1 An initial spike is believed to increase the nucleation rate of. .. resulting in larger amounts of C54-TiSi2 Page 83 Study of Titanium Silicide Formation using Spike Anneal After the formation of the C54-TiSi2 phase during the spike anneal, the growth of C54-TiSi2 grains are thermodynamically more favorable over that of the C49-TiSi2 phase However, this is not to claim that C49-TiSi2 does not continue to form after the spike anneal Even if there was insufficient thermal budget... in all cases The activation energy for the formation of the C49-TiSi2 phase was obtained and found to be in a range of 1.53 ~2. 04 eV With increasing Si substrate amorphization the activation energy increases initially before it decreases A second exothermic peak was recorded in the DSC traces when there was a sufficient degree of Si substrate amorphization This new peak occurs before the formation of. .. therefore would have acted as a compressive layer on any TiSi2 formed This is because both the C54-TiSi2 phase (14.3 x 10-6 K-1) and the C49-TiSi2 phase ( 12. 0 x 10-6 K-1)[ 52] have higher thermal expansion coefficients than the TiN phase(9.35 x 10-6 K-1)[53] During heating, TiSi2 expands more than TiN, and therefore gets compressed by the TiN The presence of a compressive capping layer would then help . Study of Titanium Silicide Formation using Spike Anneal Chapter 5 Study of Titanium Silicide Formation using Spike Anneals 5.1 Introduction To extend the usefulness of TiSi 2 , integrated chip. deviation indicating a mixture of C49/C54 TiSi 2 phases. As compared to specimen A Page 73 Study of Titanium Silicide Formation using Spike Anneal in Figure 5 -2( a), the sheet resistance remains. amounts of C54-TiSi 2 . Page 83 Study of Titanium Silicide Formation using Spike Anneal After the formation of the C54-TiSi 2 phase during the spike anneal, the growth of C54-TiSi 2 grains