High-performance MIM capacitor using ALD high-k HfO2-Al2O3 laminate dielectrics

730 IEEE ELECTRON DEVICE LETTERS, VOL. 24, NO. 12, DECEMBER 2003

High-Performance MIM Capacitor Using ALD

High-

 HfO

₂

–Al

₂

O

₃

Laminate Dielectrics

Shi-Jin Ding, Hang Hu, H. F. Lim, S. J. Kim, X. F. Yu, Chunxiang Zhu, Member, IEEE, M. F. Li, Senior Member, IEEE,

Byung Jin Cho, Senior Member, IEEE, Daniel S. H. Chan, Senior Member, IEEE, Subhash C. Rustagi, M. B. Yu,

Albert Chin, Senior Member, IEEE, and Dim-Lee Kwong

Abstract—For the first time, we successfully fabricated and

demonstrated high performance metal–insulator–metal (MIM) capacitors with HfO₂–Al₂O₃ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF m2from 10 kHz up to 20 GHz, very low leakage current of 3.2 10 8 A/cm2at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm 2, temperature coefficient of capacitance of 182 ppm C, and high breakdown field of 6 MV/cm as well as promising reli-ability. As a result, the HfO₂–Al₂O₃laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications.

Index Terms—Atomic layer deposition (ALD), HfO₂–Al₂O₃ laminate, high- , metal–insulator–metal (MIM) capacitor.

I. INTRODUCTION

T

HE trend in the on-chip integrated passive devices for wireless applications triggers the demand for metal–in-sulator–metal (MIM) capacitors embedded into the interlevel dielectric layers to enhance radio frequency (RF) performance. With an increase in levels of integration and scale–down of chip size, integrated RF capacitors with higher capacitance density will be required in future technology. High capacitance density can be achieved by employing either high- materials or very thin dielectric films. However, leakage current and reli-ability issues limit the thickness scaling [1]. Therefore, high-materials are much preferred as a possible solution. Recently, various potential high- dielectrics have been investigated for the MIM capacitors [2]–[7], the challenge has been to achieve large capacitance density at RF with acceptable leakage current,

Manuscript received September 18, 2003; revised October 13, 2003. This work was supported by Institute of Microelectronics, Singapore, under Grant R-263-000-233-490 and the National University of Singapore under Grant R-263-000-221-112. The review of this letter was arranged by Editor S. Kawamura.

S.-J. Ding is with the Silicon Nano Device Laboratory, Depatment of Elec-trical and Computer Engineering, National University of Singapore, Singapore 119260. He is also with the Institute of Microelectronics, Singapore 117685.

H. Hu, H. F. Lim, S. J. Kim, X. F. Yu, C. Zhu, M. F. Li, B. J. Cho, and D. S. H. Chan are with the Silicon Nano Device Laboratory, Depatment of Electrical and Computer Engineering, National University of Singapore, Singapore 119260 (e-mail: [email protected]).

M. F. Li, S. C. Rustagi and M. B. Yu are with the Institute of Microelectronics, Singapore 117685.

A. Chin is with the Department of Electronics Engineering, National Chiao-Tung University, Hsinchu 30050, Taiwan, R.O.C.

D.-L. Kwong is with the Department of Electrical and Computer Engineering, University of Texas, Austin, TX 78712 USA.

Digital Object Identifier 10.1109/LED.2003.820664

voltage linearity and reliability under the thermal budget of back-end line process. HfO –Al O laminate has been re-ported in metal–insulator-poly-Si (MIS) capacitor for dynamic random access memory application, where low-frequency behavior of capacitance and leakage current are described particularly, showing excellent leakage characteristics and good device reliability [8]. Thus, it is desirable to employ the HfO –Al O laminate in the MIM capacitor for Si RF and analog MIM capacitor applications. In this work, we use the laminate composition of HfO (5 nm):Al O (1 nm) with 1 nm Al O as the starting and end layers, respectively. The use of 1 nm Al O as the contacting layer to the top and bottom electrodes is intended to improve the meta/dielectric interface quality. As a result, high-performance MIM capacitors using atomic layer deposition (ALD) HfO –Al O laminates have been demonstrated successfully, suggesting it to be a very promising candidate for next generation RF and mixed signal integrated circuit (IC) applications.

II. EXPERIMENTS

The HfO –Al O laminate MIM capacitors were fabricated on m deposited on SiO substrate. The bottom electrode of Ta/TaN was prepared by sputtering, where TaN is employed as a barrier layer and Ta is used to reduce the parasitic resis-tance from the electrode. The laminate containing alternate Al O (1 nm) and HfO (5 nm) layers was deposited using ALD at 320 C, and the beginning and end layers were 1 nm Al O . Here, Al O was deposited using tri-methyl aluminum and water, while HfO was deposited using HfCl and water. Two thicknesses of laminate dielectrics (i.e., 13- and 43 nm) were deposited. Subsequently, TaN was sputtered reactively as the top electrode, followed by annealing at 420 C in forming gas for 30 min to reduce leakage current. Finally, a photolithography step and dry etching were adopted to define the MIM capacitors. In consideration of RF characterization, the coplanar transmission lines were fabricated, which also served as the top and bottom electrodes; and Al was employed as the contact pads after TaN top electrode formation. The maximum temperature of 420 C in the device fabrication is compatible with the back-end line integration.

The leakage current was measured using an HP4155B semi-conductor parameter analyzer, and the capacitance was mea-sured using an HP4284A precision LCR meter with frequen-cies varying from 10 kHz to 1 MHz. For RF characterization, the scattering ( ) parameters were measured on wafer using

DING et al.: HIGH PERFORMANCE MIM CAPACITOR USING ALD HIGH- HfO –Al O LAMINATE DIELECTRICS 731

Fig. 1. Dependence of capacitance density on the frequency for 13- and 43-nm laminate MIM capacitors at zero bias.

an HP 8510C network analyzer with the GGBs air coplanar probes (ACP) for ground-signal-ground (GSG) configuration. The measured -parameters were de-embedded from a dummy device and the high-frequency capacitance plus parasitic param-eters were extracted using an equivalent circuit model and IC cap software [9].

III. RESULTS ANDDISCUSSION

Fig. 1 shows frequency dependences of capacitance densities for the 13- and 43–nm laminate MIM capacitors. It can be found that the capacitance densities are almost unchanged from 10 k to 20 GHz, indicating excellent dielectric characteristics with fre-quency. Compared to AlTiO MIM capacitor [7], the laminate MIM capacitor exhibits a significant improvement in preserva-tion of capacitance density up to 20 GHz. As evidenced from Fig. 1, the capacitance densities for the 13- and 43-nm laminate MIM capacitors are 12.8 and 4.3 m , respectively. The cal-culated dielectric constant is ~19, which is close to that of O film. Such a high capacitance density of 12.8 m can easily satisfy the RF bypass capacitor requirement till year 2007 ac-cording to the International Technology Roadmap for Semicon-ductors (ITRS) [10].

Voltage coefficients of capacitance (VCCs) are very impor-tant parameters for MIM capacitor applications, and can be ob-tained by using a second order polynomial equation of

, where is the zero-biased capacitance, and represent the quadratic and linear VCCs respectively. Fig. 2 demonstrates dc bias dependence of normalized capaci-tance . The resultant and values for different ap-plied frequencies and laminate thicknesses are also presented in Fig. 2, where it is noticed that the VCCs decrease with in-creasing the laminate thickness and the measurement frequency. As for the 13-nm laminate MIM capacitor with a capacitance density of 12.8 fF m , the value is 240 ppm/V at 1 MHz, which is sufficiently low in comparison with the required value (1000 ppm/V) for RF bypass MIM capacitor application [10]. In addition, the temperature dependent capacitance for the lam-inate MIM capacitors is also measured at 100 kHz from 25 to 125 C, the derived temperature coefficients of capacitance are

Fig. 2. DC bias dependence of normalized capacitance(1C=C ) at 100 k and 1 MHz for 13- and 43-nm laminate MIM capacitors.

Fig. 3. Leakage current versus dc bias for the 13- and 43-nm laminate MIM capacitors. The insert illustrates the cumulative probability dependent on breakdown voltage of the MIM capacitors with two thicknesses of laminate.

182 and 199 ppm C for the 13- and 43-nm laminate MIM ca-pacitors, respectively.

Fig. 3 presents the typical – characteristics of the 13-and 43-nm laminate MIM capacitors. Regarding our inter-ested 13-nm laminate MIM capacitor, the leakage current is 3.2 A/cm at 3.3 V in the case of room temperature, and reaches 7.5 A/cm at 3.3 V at the measurement temperature of 125 C, which is markedly superior to ALD HfO and PVD Tb-doped HfO MIM capacitors [3], [4]. On the other hand, the leakage current can be reduced further by optimization of the laminate composition, as suggested by Kukli et al. [12]. In addition, the inset in Fig. 3 shows that the breakdown voltage distributions of the laminate capacitors are narrow and consistent. With regard to the 13- and 43-nm lami-nate MIM capacitors, the corresponding breakdown voltages at 25 C are around 7.7 and 25.6 V MV/cm , respectively. Such low leakage currents and high breakdown voltages are most likely attributed to the incorporations of thin amorphous Al O layers, which exploit the merits of large band gap of Al O thereby reducing the leakage and slow oxygen diffusion

732 IEEE ELECTRON DEVICE LETTERS, VOL. 24, NO. 12, DECEMBER 2003

(a) (b)

Fig. 4. (a) Cumulative TDDB curves under various constant voltage stressing for 13-nm laminate MIM capacitor measured at room temperature (b) Lifetime projection of 13-nm laminate MIM capacitor, using 50% failure time as the criteria from (a).

TABLE I

COMPARISON OFVARIOUSHIGHCAPACITANCEDENSITYMIM CAPACITORS USINGHIGH- DIELECTRICS(YEAR2002–2003)

through Al-O matrix improving the interface properties [11]. At the same time, the intermediate amorphous Al O layers terminate the continuous crystal growth of HfO , thereby eliminate the grain boundary channels extending from one electrode to the other, which is responsible for the reduced con-ductivity [12]. Additionally, using ALD technique can achieve stoichiometric dielectric films [13], likely enhancing dielectric performance compared to reactively sputtered dielectrics.

The lifetime of the 13-nm laminate MIM capacitor has also been accessed using 1 cm size devices at room tem-perature. Time to breakdown characteristics of the 13-nm lam-inate MIM capacitors were evaluated under different constant voltage stress, as shown in Fig. 4(a). The projection of the op-erating voltage for a 10-year lifetime is 3.3 V by taking the as the failure criterion, as illustrated in Fig. 4(b). It in-dicates that the HfO –Al O laminate MIM capacitors are of promising reliability, even though obtained at room tempera-ture, for practical applications. Finally, Table I compares our re-sults on HfO –Al O laminate MIM capacitors with other high capacitance density MIM capacitors reported recently [2]–[4], [6], it is shown that the laminate MIM capacitors exhibit nearly

the best electrical performance as well as promising device re-liability, suggesting it as a good candidate for next generation MIM capacitor application.

IV. CONCLUSION

High-performance ALD HfO –Al O laminate MIM capac-itors have been demonstrated for the first time. Compared with various high- MIM capacitors, our data shows that the laminate MIM capacitor exhibits superior electrical characteristics such as high capacitance density at RF regime, low leakage current and linear VCC, high breakdown field plus promising device re-liability. All these indicate that the O –Al O laminate is a very promising dielectric for MIM capacitors in Si analog and RF IC applications.

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