RECENTLY, as the use of metal/high-k dielectric has

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1 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 60, NO. 11, NOVEMBER Intrinsic Time Zero Dielectric Breakdown Characteristics of HfAlO Alloys Jin Ju Kim, Minwoo Kim, Ukjin Jung, Kyung Eun Chang, Sangkyung Lee, Yonghun Kim, Young Gon Lee, Rino Choi, Senior Member, IEEE, and Byoung Hun Lee, Senior Member, IEEE Abstract A thermochemical model describing the relationship between the dielectric breakdown field (E BD ) and dielectric constant(k) of high-k dielectric has been calibrated for Hf x Al 1 x O y alloys with k values from 7 to 24. Metal-insulatormetal (MIM) capacitors with Hf x Al 1 x O y high-k dielectric films were used to extract the intrinsic time zero dielectric breakdown characteristics. Breakdown field values of these Hf x Al 1 x O y alloys were found to decrease as a function of k 0.77 while the electric field acceleration parameter, γ, increases as a function of k Using the thermochemical model calibrated with the experimental data, a Hf x Al 1 x O y 10-year lifetime was extrapolated as a function of the dielectric constant to provide insight for future dielectric development. Index Terms Al 2 O 3, breakdown field, dielectric constant, HfO 2, lifetime, MIM capacitor, thermochemical model, time-dependent dielectric breakdown (TDDB). I. INTRODUCTION RECENTLY, as the use of metal/high-k dielectric has become more prevalent in state-of-the-art semiconductor devices, the reliability characteristics of high-k dielectrics have attracted attention [1] [5]. Even much research has addressed the reliability of specific material systems or devices using high-k dielectrics, the study of the intrinsic reliability characteristics of high-k dielectrics has been limited because their material composition and integration processes are so diverse, depending on specific applications. Compared with the decades-long debates on the intrinsic reliability mechanisms of SiO 2 -based gate dielectric, it is evident that the intrinsic reliability characteristics of high-k dielectric have not been sufficiently explored [6] [9]. Studying the intrinsic reliability characteristics of high-k dielectric is difficult, however, because high-k dielectric is Manuscript received May 9, 2013; revised September 6, 2013; accepted September 9, Date of publication September 30, 2013; date of current version October 18, This work was supported in part by SAMSUNG System LSI, and in part by the Industrial Strategic Technology Development Program under Grant funded by MOTIE and KEIT, Korea. The review of this paper was arranged by Editor M. J. Kumar. J. J. Kim is with the Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology, Gwangju , Korea ( starlet1201@gist.ac.kr). M. Kim, U. Jung, K. E. Chang, S. Lee, Y. Kim, Y. G. Lee, and B. H. Lee are are with the School of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju , Korea ( kmw@gist.ac.kr; ukjin@gist.ac.kr; eun@gist.ac.kr; leesk@gist.ac.kr; kyhun09@gist.ac.kr; nicehack@gist.ac.kr; bhl@gist.ac.kr). R. Choi is with the Department of Material Science and Engineering, Inha University, Incheon , Korea ( rino.choi@inha.ac.kr). Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /TED IEEE usually stacked on a SiO x -based interfacial layer, which grows naturally during the gate stack process. As a result, interface-driven reliability characteristics such as negative bias temperature instability (NBTI) are found to depend on the quality of the interfacial SiO x layer [10] [14]. Furthermore, much previous work on the reliability of high-k dielectrics has focused on the reliability characteristics of the high-k dielectric/interfacial layer stack without an explicit understanding of the intrinsic reliability characteristics of the high-k dielectric itself [15] [17]. However, as the scaling of high-k dielectric goes into the sub-1 nm equivalent oxide thickness (EOT) regime, the thickness of the interfacial layer must be further scaled and reliability characteristics become dominated by the high-k dielectric rather than the interfacial layer. Thus, a systematic understanding of the intrinsic reliability of the high-k dielectric layer becomes more important. In particular, an accurate breakdown model of the high-k dielectric is necessary to develop a lifetime prediction model for high-k dielectric/sio x interfacial layer stacks. With SiO 2 -based gate dielectric, various time-dependent dielectric breakdown (TDDB) models have been suggested, including an E-model (based on thermochemical models), 1/E model, power law model, and combined E and 1/E model [18] [21]. The controversy over whether the E model was preferable to the 1/E model ended with the introduction of a power law model as the thickness of SiO 2 -based dielectric decreased to the 1 nm scale. On the other hand, there is not yet consensus on a lifetime extrapolation model for high-k dielectric. Most current research on the lifetime projection of high-k dielectrics relies on the E-model or the power-law model, which matches reasonably well with experimental data [2], [22], [23]. Wu et al. [24] reported that the anode hydrogen release (AHR) model can be applied to high-k dielectric/sio x bilayer stacks and the power law model fits well for lifetime extrapolation. On other hand, Pae et al. reported that the E-model fits their experimental data for a high-k/sio x gate stack implemented in 32 nm and 45 nm technology [2]. In other instances, the E model was used in the low field region and 1/E model was used in the high field region for 45 nm high-k gate process technology [25]. While the above work is founded on the lifetime projection models developed for SiO 2 -based gate dielectric, there are a few attempts to consider the unique material properties of high-k dielectrics in the reliability research. McPherson et al. [27] claimed that the high-k dielectric itself may follow

2 3684 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 60, NO. 11, NOVEMBER 2013 a field-driven breakdown model, i.e., the thermochemical model, as the electronic bonding of the high-k dielectric is weak and more polarized than SiO 2 [26], [27]. Lee et al. [26] suggested that field-driven breakdown dominates the reliability of the high-k dielectric. The thermochemical model was discarded because it could not explain the TDDB characteristics of extremely thin SiO 2 -based dielectric [28], but this model may work for high-k dielectric because the metal-oxygen bonds are much weaker than Si-O bonds [29]. According to the thermochemical model, the breakdown field, E BD, should decrease approximately at k 0.64 for high-k materials while the field acceleration parameter, γ, should increase with k n [27], [30]. This means that the time zero dielectric breakdown (TZDB) characteristics improve with a lower-k dielectric, but the lifetime projection at low field improves more rapidly with a higher-k dielectric. The validity of this model was verified using the breakdown field data for high-k dielectrics with k values ranging from 3.9 to 300 [29]. Since the thermochemical model has provided a reasonable prediction of the breakdown field of high-k dielectrics, it is worth reexamining its accuracy with medium-k gate dielectrics with k ranging from 7 to 24, which is frequently used in practical applications. In this paper, the intrinsic reliability characteristics of Hf x Al 1 x O y dielectric were investigated to extract parameters to calibrate the thermochemical model. The 10-year lifetime of Hf x Al 1 x O y dielectric was then extrapolated using the calibrated thermochemical breakdown model. II. EXPERIMENT Metal-insulator-metal (MIM) capacitors with a Hf x Al 1 x O y dielectric layer were fabricated using Pt bottom electrodes. The ternary composite films composed of different ratios of HfO 2 and Al 2 O 3 were formed by controlling the ratios of the RF magnetron sputtering power (power density = W/cm 2 ) for a 4 in target. Post-deposition annealing (PDA) was performed in pure O 2 ambient for 5 minutes at 400 C to control the oxygen stoichiometry. Then, the top Pt electrode was deposited with a shadow mask using RF magnetron sputtering at room temperature, followed by N 2 gas annealing at 400 C for 30 min. The area of device was in a range of 5E-5 cm 2 to1e-4 cm 2. Table I summarizes the physical and electrical properties of the samples used in this paper. The capacitance-voltage (C V ) characteristics of the MIM capacitors were characterized using a precision impedance analyzer at frequencies from 100 khz to 1 MHz. For MIM capacitor, EOT is simply calculated from the capacitance measured at 0 V, 1 MHz using EOT = k SiO2 A/capacitance. The physical thicknesses of Hf x Al 1 x O y in the MIM capacitors were measured using a transmission electron microscope (TEM) as shown in Fig. 1. In this paper, thick Hf x Al 1 x O y films (T phys = 8 23 nm) were used to obtain the intrinsic reliability characteristics with minimal interference from excessive leakage current. The dielectric constant was calculated using the capacitance at 0 V and the physical thickness (T phys ). Finally, the concentration of aluminum in each film was analyzed using an energy dispersive X-ray (EDX) method. TABLE I CHARACTERISTICS OF DIELECTRICS USED IN THIS PAPER Fig. 1. TEM images of MIM capacitors with Hf x Al 1 x O y dielectrics. Physical thicknesses measured with TEM are listed in Table I. Leakage current and TZDB characteristics were measured using a parameter analyzer at room temperature. The voltage ramp rate was fixed at 0.15 s for 10 mv steps (67 mv per second) during the time zero breakdown test. Breakdown voltage (V BD ) was defined as the stress bias at which the leakage current abruptly increased by more than an order of magnitude. The breakdown field, E BD,was calculated using V BD /T phys (MV/cm). For each split shown in Table I, more than 20 devices were tested and the results averaged. III. RESULTS AND DISCUSSION The MIM capacitors with Hf x Al 1 x O y dielectrics showed well behaved current-voltage (I V ) curves [Fig. 2(a)]. The leakage current injected from the top electrode side (negative bias region) appears to be slightly lower than the other polarity, but J g curves are reasonably symmetric. Since the physical thickness measured by TEM varied from 8 nm to 23 nm for different compositions, the level of the leakage current cannot be directly compared using J g curves. For more meaningful comparison to illustrate the robustness of the dielectrics, the leakage current density was plotted as a function of EOT at +1 V with the data reported in the literature (Fig. 2(b)) [31] [34]. The leakage current density of Hf x Al 1 x O y

3 KIM et al.: INTRINSIC TIME ZERO DIELECTRIC BREAKDOWN CHARACTERISTICS OF HfAlO ALLOYS 3685 Fig. 4. Weibull distributions of E BD for high-k dielectric with k = 14.5 normalized for different areas nicely overlap each other, demonstrating a uniform degradation. Inset: graph showing the area dependence of the breakdown field at 63%. Fig. 2. (a) Typical J g V g curves for each dielectric split shown in Table I. (b) Leakage current density measured at +1 V for different dielectric thicknesses. Reference MIM devices used a TiN electrode while a Pt electrode wasusedinthispaper. Fig. 5. Breakdown field versus dielectric constant. Filled squares are experimental data for Hf x Al 1 x O y. Empty circles represent the E BD calculated using the thermochemical model. Filled triangles are experimental data reported by McPherson et al. [29]. Fig. 3. (a) Typical J g curves showing the TZDB characteristics at room temperature. (b) Weibull distribution of the breakdown field of high-k dielectric with k ranging from The slope, β, of the Weibull curves varies within dielectrics is comparable or better than other MIM dielectrics, indicating that the PDA and final N 2 anneal at 400 C work well to densify the MIM dielectric. These dielectrics therefore qualified for the reliability assessment. E BD values were extracted from the I V curves shown in Fig. 3(a). Since the x-axis of Fig. 3(a) is the electric field, the representative J g curves show that the breakdown field is inversely proportional to the dielectric constant. For quantitative comparison, the E BD values measured in high-k dielectrics with different dielectric constants are summarized using the Weibull plot shown in Fig. 3(b). Most of the Hf x Al 1 x O y splits exhibited a steep single slope with a tight distribution, indicating the breakdown events were driven by a single breakdown mechanism. The robustness of the dielectric used in this paper was confirmed again by measuring the E BD of devices with different areas. Fig. 4 shows that the area-normalized Weibull distributions of E BD for Hf x Al 1 x O y with k = 14.5 overlap each other, demonstrating a uniform degradation mechanism, i.e., a uniform distribution of weak spots [35], [36]. The inset of Fig. 4 shows that the intrinsic E BD value taken at the 63% accumulative values of the Weill distribution decreases as the area increased from to cm 2. As the area increases, the number of weak spots also increases and device failure occurs at a lower field. Therefore, in this paper, the smallest device area of cm 2 was used to obtain more intrinsic breakdown characteristics. Intrinsic E BD values taken at 63% accumulative values of the Weibull plot showed a well behaved trend curve as a function of the dielectric constant as seen in Fig. 5,

4 3686 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 60, NO. 11, NOVEMBER 2013 which contains more data points than Table I because the thickness split for each composition yielded slight variations in k and E BD. As the Al concentration increases (i.e., as the k value decreases), the E BD also increases. The E BD of Al 2 O 3 was 7.3 MV/cm, which is much lower than the E BD of bulk Al 2 O 3 predicted by the thermochemical model (tetrahedral/tetragonal: 11.2 MV/cm, trigonal: 13.8 MV/cm), but matches the E BD values reported in the literature [37]. On the other hand, the E BD of HfO 2 was similar to the bulk E BD values (tetrahedral/tetragonal: 3.3 MV/cm, cubic: 4 MV/cm). The dielectric constant of Al 2 O 3 around 7 indicates that the Al 2 O 3 used in this paper is partially amorphous because the dielectric constant of crystalline Al 2 O 3 is 9. On the other hand, the HfO 2 seems to be well crystalized. This observation matches reports on the crystallinity of sputterdeposited Al 2 O 3 and HfO 2. In the thermochemical model, E BD values can be calculated by the following equation [29]: E BD (k) = H 0 ( P 2+k n ) k 0.77 (1) 0 3 where H 0 * is the activation energy, P 0 is the active molecular dipole moment, k is the dielectric constant, and n is a fitting parameter to obtain a generalized k-dependence. H 0 * can be calculated for a specific high-k dielectric, but it is difficult to obtain exact values for alloyed high-k dielectric such as Hf x Al 1 x O y. In this paper, H 0 * was calculated from (1) using the experimental E BD values listed in Table I. The P 0 values of Hf x Al 1 x O y were interpolated from those of Al 2 O 3 and HfO 2. Underlying assumption of this interpolation is that E BD values of alloyed high-k dielectric are determined by the composition as shown in Fig. 5. The E BD values of Hf x Al 1 x O y shown in Fig. 5 decreased as a function of k 0.77, which is similar to previously reported values (k 0.65 ) [29]. The E BD (k) of Hf x Al 1 x O y was slightly lower than the theoretical prediction using the thermochemical model because the dielectric constant of Al 2 O 3 used in this paper is slightly lower than the theoretical value of tetrahedral Al 2 O 3. Since the thermochemical E BD model representing the general trend was developed for an extremely wide range of k values (k = ) with scattered data shown as empty circles in Fig. 5 and only a few data points in the low-k to medium-k region, a slight difference in the E BD in the medium-k region is expected. The calibrated E BD (k) function matches well with experimental data and can be used to represent the intrinsic reliability of specific material systems such as Hf x Al 1 x O y. The excellent predictability of the calibrated E BD (k) for Hf x Al 1 x O y indicates that the lifetime of high-k dielectric can be predicted using the thermochemical model because the field-induced bond breaking mechanism may lead to a lifetime extrapolation model different from that of SiO 2 -based gate dielectrics. Thus, we attempted to derive the TDDB characteristics using the TZDB characteristics, i.e., the E BD (k) function, using the Berman model. According to the Berman model, the breakdown field, distributions can be translated into time-to-failure (TF) distributions [38] ( TF = t 0 exp γ E+ H ) 0 = t 0 exp [ γ (E BD E OX ) ]. (2) k B T Here, t 0 is an effective time at field = 1/(γ ramp rate), k B is the Boltzmann s constant, T is the temperature, ΔH 0 * is the activation energy, E ox is the applied field to the capacitor, and E BD is the breakdown field listed in Table I. For a SiO 2 capacitor, 0.1 sec is used for t 0 [29]. Since t 0 is determined by the acceleration factor (γ) and the ramp rate (R), it is dependent on the dielectric constant at a constant ramp rate. As a result, as shown in (2), E BD is affected by the ramp rate. In this paper, t 0 values listed in Table I were extracted using a ramp rate of (V/cm sec) for each acceleration factor. For Hf x Al 1 x O y lifetime predictions, several assumptions were applied to the TDDB model. First, the structure of Hf x Al 1 x O y was assumed to be tetrahedral/tetragonal to set a reference point using the P 0 value of Al 2 O 3 (tetrahedral/ tetragonal: 2.9 e-å, trigonal: 7 e-å) and of HfO 2 (tetrahedral/ tetragonal: 4.4 e-å, cubic: 10.2 e-å). This assumption is reasonable for crystalline HfO 2.ForAl 2 O 3, the theoretical E BD calculated using the P 0 value for crystalline Al 2 O 3 was higher than the experimental E BD. This means that the experimental P 0 should be slightly larger than the theoretical P 0 to yield lower E BD. This error will yield a slightly underestimated γ(k) for Hf x Al 1 x O y because γ, a field acceleration parameter, is calculated using a molecular model as shown below [27], [30], [33], [38] ( ) P 2+k n 0 3 γ = k (3) k B T The γ values of Hf x Al 1 x O y at 300 K are calculated using the interpolated P 0 and k n values calibrated for Hf x Al 1 x O y. Resulting γ values show an k 1.37 dependence. The high field acceleration parameter for higher-k dielectrics means that the lifetime of the high-k dielectric increases rapidly under low field stress conditions. To illustrate the relationship between E BD and lifetime, TF values were calculated as a function of an operation field, E ox,usinge BD (k) and γ(k) calibrated for Hf x Al 1 x O y and (2) as shown in Fig. 6(a). The maximum operation field allowing for 10-year operation is nearly independent of dielectric constant even though the E BD degrades as k increases due to the weak metal-oxygen bond. Fig. 6(b) shows the maximum E ox values to achieve a 10-year lifetime plotted as a function of k. E ox,max is found to be 2MV/cm for 7 < k < 24 and very weakly dependent on dielectric thickness because the operation field, E ox,isdefined as the gate voltage divided by the dielectric physical thickness (E ox = V g /T phy ).SinceE BD decreases at higher k because of more polarized bonding, the time to failure decreases rapidly for higher k as the electric field increases, i.e. more steep slope in Fig. 6(a). In other words, higher-k dielectrics less likely breakdown at a low field stress condition because the bonds can be easily stretched more instead of breaking down. Thus, the maximum breakdown field values to achieve 10 year lifetime become similar for all alloyed dielectrics as

5 KIM et al.: INTRINSIC TIME ZERO DIELECTRIC BREAKDOWN CHARACTERISTICS OF HfAlO ALLOYS 3687 Fig. 6. (a) Calculated TDDB characteristics of Hf x Al 1 x O y are plotted as a function of electric field with difference dielectric constants (k = 7 24). The TF data were extracted using E BD and γ from Table I. (b) 10-year operation field extracted from the TDDB model. Operation field E ox is defined as V g /T phy. a result of trade-off between γ and E BD.Ask increases, γ increases rapidly with k 1.37 dependence while E BD decreases with k 0.77 dependence. When the k value is low, E BD is high, but the low γ value dramatically degrades device lifetime. On the other hand, when the k value is high, the high γ values rapidly improve lifetime while E BD slowly decreases. Even though this result is based on an assumption that the breakdown of the high-k dielectric is driven by field-dependent bond breakage, the implication of this calculation is quite significant. The maximum electric field that can be applied to a given high-k dielectric with a 10-year lifetime constraint is not substantially affected by the dielectric constant of the high-k dielectric, especially in the k range examined in this paper (k = 7 24). The implication of this conclusion is more cogent if a similar calculation is performed at a fixed equivalent oxide thickness (EOT) for a specific technology node. For example, Fig. 7(a) shows a hypothetical maximum operation voltage for 10-year operation as predicted by the thermochemical model calibrated for Hf x Al 1 x O y alloys in a MIM structure at an EOT fixed at 1 nm. The predicted 10-year operation voltage gradually increases as the dielectric constant increases. This means the higher dielectric constant is beneficial for reliability. However, the dielectric leakage current increases as the dielectric constant increases because the bandgap of the dielectric decreases even though the physical thickness of the high-k dielectric increases for the fixed EOT. Fig. 7(b) shows an Fig. 7. (a) 10-year operation voltage extracted from Fig. 6(b), TDDB model, when the EOT of devices was fixed at 1 nm for devices with various dielectric constants. (b) Leakage current curve of Hf x Al 1 x O y dielectric with a similar EOT, but different k values (k = 7 and 10). example of the correlation between the k-value and leakage current. Even though the EOTs of both films are similar, nm, the leakage current is higher in the MIM capacitor with a higher-k dielectric. In summary, the TDDB characteristics of Hf x Al 1 x O y can be derived using the E BD (k) function calibrated for Hf x Al 1 x O y. Higher-k material has a better reliability window in terms of device lifetime, but the lower bandgap for higher-k dielectric causes a trade-off between reliability and the higher leakage current. In the future, the modified thermochemical model and its TDDB translation should be confirmed by extensive experimental data. Nevertheless, this theoretical projection provides guidance for future high-k dielectric development considering reliability. This approach can be used as a stepping stone to develop a general reliability model for high-k dielectrics with an interfacial layer. IV. CONCLUSION The intrinsic TZDB characteristics of Hf x Al 1 x O y have been investigated using a MIM structure, which can eliminate the influence of the interfacial layer. The E BD of Hf x Al 1 x O y decreases as a function of (k) 0.77 while γ increases with (k) Using a E BD (k) function developed for a specific high-k dielectric system, a TDDB model can be developed. Even though this TDDB model should be confirmed with extensive experimental data, this approach will provide a feasible path to develop a general reliability model for high-k dielectrics with proper consideration of the reliability of the interfacial layer.

6 3688 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 60, NO. 11, NOVEMBER 2013 REFERENCES [1] B. H. Lee, R. Choi, J. H. Sim, S. A. Krishnan, J. J. Peterson, G. A. Brown, and G. Bersuker, Validity of constant voltage stress based reliability assessment of high-k devices, IEEE Trans. Device Mater. Rel., vol. 5, no. 1, pp , Mar [2] S. Pae, A. Ashok, J. Choi, T. Ghani, J. He, S. H. Lee, K. Lemay, M. Liu, R. Lu, P. Packan, C. Parker, R. Purser, A. S. Amour, and B. Woolery, Reliability characterization of 32 nm high-k and metalgate logic transistor technology, in Proc. IEEE IRPS, May 2010, pp [3] B. H. Lee, S. C. Song, R. Choi, and P. Kirsch, Metal electrode/high-k dielectric gate-stack technology for power management, IEEE Trans. Electron Devices, vol. 55, no. 1, pp. 8 20, Jan [4] S. Pae, M. Agostinelli, M. Brazier, R. Chau, G. Dewey, T. Ghani, M. Hattendorf, J. Hicks, J. Kavalieros, K. Kuhn, M. Kuhn, J. Maiz, M. Metz, K. Mistry, C. Prasad, S. Ramey, A. Roskowski, J. Sandford, C. Thomas, J. Thomas, C. Wiegand, and J. Wiedemer, BTI reliability of 45 nm high-k + metal-gate process technology, in Proc. IEEE IRPS, May 2008, pp [5] E. Cartier, A. Kerber, T. Ando, M. M. Frank, K. Choi, S. Krishnan, B. Linder, K. Zhao, F. Monsieur, J. Stathis, and V. Narayanan, Fundamental aspects of HfO 2 -based high-k metal gate stack reliability and implications on tinv-scaling, in Proc. IEEE IEDM, Dec. 2011, pp [6] B. H. Lee, C. Kang, R. Choi, H. D. Lee, and G. Bersuker, Stress field analysis to understand the breakdown characteristics of stacked high-k dielectrics, Appl. Phys. Lett., vol. 94, no. 16, pp , Apr [7] T. Yamaguchi, I. Hirano, R. Iijima, K. Sekine, M. Takayanagi, K. Eguchi, Y. Mitani, and N. Fukushima, Thermochemical understanding of dielectric breakdown in HfSiON with current acceleration, in Proc. IEEE IRPS, Apr. 2005, pp [8] K. Torii, K. Shiraishi, S. Miyazaki, K. Yamabe, M. Boero, T. Chikyow, K. Yamada, H. Kitajima, and T. Arikado, Physical model of BTI, TDDB and SILC in HfO 2 -based high-k gate dielectrics, in Proc. IEEE IEDM, Dec. 2004, pp [9] A. Kerber, A. Vayshenker, D. Lipp, T. Nigam, and E. Cartier, Impact of charge trapping on the voltage acceleration of TDDB in metal gate/high-k n-channel MOSFETs, in Proc. IEEE IRPS, May 2010, pp [10] G. Ribes, J. Mitard, M. Denais, S. Bruyere, F. Monsieur, C. Parthasarathy, E. Vincent, and G. Ghibaudo, Review on high-k dielectrics reliability issues, IEEE Trans. Device Mater. Rel., vol. 5, no. 1, pp. 5 19, Mar [11] D. K. Schroder and J. A. Babcock, Negative bias temperature instability: Road to cross in deep submicron silicon semiconductor manufacturing, J. Appl. Phys., vol. 94, no. 1, pp. 1 18, Jul [12] W. Wang, V. Reddy, A. T. Krishnan, R. Vattikonda, S. Krishnan, and Y. Cao, Compact modeling and simulation of circuit reliability for 65-nm CMOS technology, IEEE Trans. Device Mater. Rel., vol. 7, no. 4, pp , Dec [13] A. Neugroschel, G. Bersuker, R. Choi, C. Cochrane, P. Lenahan, D. Heh, C. Young, C. Y. Kang, B. H. Lee, and R. Jammy, An accurate lifetime analysis methodology incorporating governing NBTI mechanisms in high-k/sio 2 gate stacks, in Proc. IEDM, Dec. 2006, pp [14] M. Cho, M. Aoulaiche, R. Degraeve, B. Kaczer, J. Franco, T. Kauerauf, P. Roussel, L. Å. Ragnarsson, J. Tseng, T. Y. Hoffmann, and G. Groeseneken, Positive and negative bias temperature instability on sub-nanometer EOT high-k MOSFETs, in Proc. IEEE IRPS, May 2010, pp [15] T. Nigam, A. Kerber, and P. Peumans, Accurate model for timedependent dielectric breakdown of high-k metal gate stacks, in Proc. IEEE IRPS, Apr. 2009, pp [16] D. Y. Choi, K. T. Lee, C. K. Baek, C. W. Sohn, H. C. Sagong, E. Y. Jung, J. S. Lee, and Y. H. Jeong, Interfacial-layer-driven dielectric degradation and breakdown of HfSiON/SiON gate dielectric nmosfets, IEEE Electron Device Lett., vol. 32, no. 10, pp , Oct [17] M. Jo, C. Y. Kang, J. Huang, G. Bersuker, C. Young, P. Kirsch, and R. Jammy, Improved high-k/metal gate lifetime via improved SILC understanding and mitigation, in Proc. IEEE IEDM, Dec. 2011, pp [18] J. McPherson, V. Reddy, K. Banerjee, and H. Le, Comparison of E and 1/E TDDB models for SiO 2 under long-term/low-field test conditions, in Proc. IEEE IEDM, Dec. 1998, pp [19] E. Rosenbaum, J. C. King, and C. Hu, Accelerated testing of SiO 2 reliability, IEEE Trans. Electron Devices, vol. 43, no. 1, pp , Jan [20] E. Y. Wu, A. Vayshenker, E. Nowak, J. Suñé, R. P. Vollertsen, W. Lai, and D. Harmon, Experimental evidence of TBD powerlaw for voltage dependence of oxide breakdown in ultrathin gate oxides, IEEE Trans. Electron Devices, vol. 49, no. 12, pp , Dec [21] C. Hu and Q. Lu, United gate oxide reliability model, in Proc. IEEE IRPS, May 1999, pp [22] T. Kauerauf, R. Degraeve, L. Å. Ragnarsson, P. Roussel, S. Sahhaf, G. Groeseneken, and R. O Connor, Methodologies for sub-1 nm EOT TDDB evaluation, in Proc. IEEE IRPS, Apr. 2011, pp. 2A.2.1 2A [23] K. T. Lee, H. Kim, and J. Park, Gate stack process optimization for TDDB improvement in 28 nm high-k/metal gate nmosfets, in Proc. IEEE IRPS, Apr. 2012, pp. GD.2.1 GD.2.4. [24] E. Wu, J. Suñé, C. Larow, and R. Dufresne, Temperature dependence of TDDB voltage acceleration in high-k/ SiO 2 bilayers and SiO 2 gate dielectrics, in Proc. IEEE IEDM, Dec pp [25] C. Prasad, M. Agostinelli, C. Auth, M. Brazier, R. Chau, G. Dewey, T. Ghani, M. Hattendorf, J. Hicks, J. Jopling, J. Kavalieros, R. Kotlyar, M. Kuhn, K. Kuhn, J. Maiz, B. McIntyre, M. Metz, K. Mistry, S. Pae, W. Rachmady, S. Ramey, A. Roskowski, J. Sandford, C. Thomas, C. Wiegand, and J. Wiedemer, Dielectric breakdown in a 45 nm high-k/metal gate process technology, in Proc. IEEE IRPS, May 2008, pp [26] B. H. Lee, C. Y. Kang, P. Kirsch, D. Heh, C. D. Young, H. B. Park, J. W. Yang, G. Bersuker, S. Krishnan, R. Choi, and H. D. Lee, Electric-field-driven dielectric breakdown of metalinsulator-metal hafnium silicate, Appl. Phys. Lett., vol. 91, no. 24, pp , Dec [27] J. W. McPherson, R. B. Khamankar, and A. Shanware, Complementary model for intrinsic time-dependent dielectric breakdown in SiO 2 dielectrics, J. Appl. Phys., vol. 88, no. 9, pp , Nov [28] E. Y. Wu and J. Suñé, Power-law voltage acceleration: A key element for ultra-thin gate oxide reliability, Microelectron. Rel., vol. 45, no. 12, pp , Dec [29] J. W. McPherson, J. Kim, A. Shanware, H. Mogul, and J. Rodriguez, Trends in the ultimate breakdown strength of high dielectric-constant materials, IEEE Trans. Electron Devices, vol. 50, no. 8, pp , Aug [30] J. W. McPherson and H. C. Mogul, Underlying physics of the thermochemical e model in describing low-field time-dependent dielectric breakdown in SiO 2 thin films, J. Appl. Phys., vol. 84, no. 3, pp , Aug [31] B. H. Lee, L. Kang, W.-J. Qi, R. Nieh, Y. Jeon, K. Onishi, and J. C. Lee, Ultrathin hafnium oxide with low leakage and excellent reliability for alternative gate dielectric application, in Proc. IEDM, Dec. 1999, pp [32] K. Takeda, R. Yamada, T. Imai, T. Fujiwara, T. Hashimoto, and T. Ando, Characteristic instabilities in HfAlO metal insulator metal capacitors under constant-voltage stress, IEEE Trans. Electron Devices, vol. 55, no. 6, pp , Jun [33] S. B. Chen, C. H. Lai, A. Chin, J. C. Hsieh, and J. Liu, High-density MIM capacitors using Al 2 O 3 and AlTiO x dielectrics, IEEE Electron Device Lett., vol. 23, no. 4, pp , Apr [34] S. J. Kim, B. J. Cho, M. F. Li, X. F. Yu, C. X. Zhu, A. Chin, and D. L. Kwong, PVD HfO 2 for high-precision MIM capacitor applications, IEEE Electron Device Lett., vol. 24, no. 6, pp , Jun [35] A. Kerber, L. Pantisano, A. Veloso, G. Groeseneken, and M. Kerber, Reliability screening of high-k dielectrics based on voltage ramp stress, Microelectron. Rel., vol. 47, nos. 4 5, pp , Apr [36] J. H. Stathis, Percolation models for gate oxide breakdown, J. Appl. Phys., vol. 86, no. 10, pp , Nov [37] J. Yota, H. Shen, and R. Ramanathan, Characterization of atomic layer deposition HfO 2,Al 2 O 3, and plasma-enhanced chemical vapor deposition Si 3 N 4 as metal insulator metal capacitor dielectric for GaAs HBT technology, J. Vac. Sci. Technol. A, vol. 31, no. 1, pp. 01A A134-9, Jan [38] A. Berman, Time-zero dielectric reliability test by a ramp method, in Proc. IEEE 19th Annu. IRPS, Apr. 1981, pp

7 KIM et al.: INTRINSIC TIME ZERO DIELECTRIC BREAKDOWN CHARACTERISTICS OF HfAlO ALLOYS 3689 Jin Ju Kim received the M.S. degree in materials science and engineering from the Gwangju Institute of Science and Technology, Gwangju, Korea, in 2010, where she is currently pursuing the Ph.D. degree in nanobiomaterials and electronics. Yonghun Kim received the M.S. degree in material science and engineering from Gwangju Institute of Science and Technology, Gwangju, Korea, in 2011, where he is currently pursuing the Ph.D. degree in material science and engineering. Minwoo Kim received the M.S. degree from the Department of Nanobio Material and Electronic, Gwangju Institute of Science and Technology, Gwangju, Korea, in 2013, where he is currently pursuing the Ph.D. degree in materials science and engineering. Young Gon Lee received the M.S. degree in material science engineering from the University of Seoul, Seoul, Korea, in He is currently pursuing the Ph.D. degree in material science and engineering, Gwangju Institute of Science and Technology, Gwangju, Korea. Ukjin Jung received the M.S. degree in material science and engineering from the Gwangju Institute of Science and Technology, Gwangju, Korea, in 2012, where she is currently pursuing the Ph.D. degree in material science and engineering. Kyung Eun Chang is currently pursuing the Integrated M.S. and Ph.D. degrees in material science and engineering with the Gwangju Institute of Science and Technology, Gwangju, Korea. Rino Choi (M 04 SM 05) received the Ph.D. degree in materials science and engineering from the University of Texas, Austin, TX, USA, in He has been with the School of Materials Science and Engineering, Inha University, Incheon, Korea, since Sangkyung Lee received the M.S. degree in nanobiomaterials and electronics from the Gwangju Institute of Science and Technology, Gwangju, Korea, in 2011, where he is currently pursuing the Ph.D. degree in materials science and engineering. Byoung Hun Lee (M 97 SM 05) received the Ph.D. degree in electrical and computer engineering from the University of Texas at Austin, Austin, TX, USA, in His current research interests include extreme lowpower device technology using novel graphenebased devices and silicon devices.