Development of New TiN/ZrO 2 /Al 2 O 3 /ZrO 2 /TiN Capacitors Extendable to 45nm Generation DRAMs Replacing HfO 2 based Dielectrics Deok-Sin Kil, Han-Sang Song, Kee-Jeung Lee, Kwon Hong, Jin-Hyock Kim, Ki-Seon Park, Seung-Jin.Yeom, Jae-Sung Roh, Noh-Jung Kwak, Hyun-Chul Sohn, Jin-Woong Kim, and Sung-Wook Park R&D Division, Hynix Semiconductor Inc., San 136-1, Ami-ri, Bubal-eub, Icheon-si, Kyoungki-Do, 467-701, KOREA Abstract New ZrO 2 /Al 2 O 3 /ZrO 2 (ZAZ) dielectric film was theoretically designed and successfully demonstrated to be applicable to 45nm DRAM devices. ZAZ dielectric film is a combined structure from tetragonal ZrO 2 and amorphous Al 2 O 3 . Thus prepared ZAZ TIT capacitors showed very small Tox.eq value of 6.3Å and low leakage current less than 1fA/cell. It was also confirmed that ZAZ TIT capacitor was thermally robust during backend full thermal process by applying it to the final DRAM product in mass production. Keywords: TIT Capacitor, ZrO 2 , Al 2 O 3 , ALD. Introduction Fig.1 shows the variation of Tox.eq values for each generation DRAM devices with storage node height. Very small Tox.eq of 6~7Å is required in order to obtain 25fF/cell for 45nm DRAM device. However, it is not possible to get that small Tox.eq with HfO 2 related materials like HfO 2 /Al 2 O 3 stack and Hf x Al y O z [1] which have been commonly used until 70nm level. Recently, it has been reported that single ZrO 2 could be applied for 50nm DRAM devices just in planar type capacitor.[2] In that report, tetragonal ZrO 2 thin films were reported to be formed by atomic layer deposition(ALD) showing high dielectric constant. However, we actually found that ZrO 2 TIT capacitor could not be easily used mainly due to the degradation in negative biased leakage current during full post thermal process as shown in Fig.2. While many researches on new electrode materials like Ru are underway in order to obtain lower Tox.eq and leakage current, it is thought that Ru technology is not matured enough due to some problems. Considering all these situations, new dielectric materials are absolutely required for 45nm DRAM generation especially extending the use of TiN electrode. In this work, we designed very characteristic dielectric film structures from ZrO 2 and Al 2 O 3 and successfully demonstrated that it could be applicable to the real DRAM devices especially mass production-wise and extendable to 45nm generation. Results and Discussion In our work, ZrO 2 films were deposited from Zr(NEtMe) 4 and ozone as precursor and oxidant respectively by ALD. Rms value of ZrO 2 thin films was drastically increased from a certain critical thicknesses, which decreased as the increase of growth temperature during deposition.(Fig.3) This abrupt increase in roughness was thought to be closely associated with the crystallization considering from inset TEM images. This data could be positively interpreted that crystalline ZrO 2 film having higher dielectric constant than amorphous one can be formed by regulating growth temperature. It has been previously reported that dielectric constant of ZrO 2 is very dependent on crystal structures like monoclinic, cubic or tetragonal phase.[3] So we checked to see if we could control the crystallinity and crystal structures as shown in Fig.4. Figure (a) shows the XRD patterns of around 30Å thick films with growth temperatures. While sufficient crystallization did not occur at 250℃, tetragonal phase became dominant at higher temperatures as well as crystallization. We could also found that crystallization and tetragonal phase could be promoted by adding extra ozone feeding step in ALD gas feeding cycle as shown in Fig.4 (b). Dielectric property of ZrO 2 films deposited at 250℃ was evaluated indirectly down to 30Å by using [Al 2 O 3 (50Å)/ZrO 2 ] TIT capacitor as shown in Fig. 5. We could observe three different regimes with thickness, <40Å, 40~50Å and >50Å. Considering the difference of slope, this behavior is considered to be originated from the crystallization of ZrO 2 films at 40~50Å, which is referred to as mixed regime. From the above understanding on the nature of ZrO 2 , we designed new film structure as shown in Fig.6. The concept was based on that higher dielectric and low leakage property could be realized by tetragonal ZrO 2 and interlaying amorphous Al 2 O 3 . New film structure by our intention was possible just by inserting 4 ALD cycles (3~5Å) of Al 2 O 3 showing crystal ZrO 2 and smooth surface as can be seen in Fig.7. Fig.8 shows the cell capacitance of Z(40Å)/A(5Å)/Z(40Å) with growth temperatures and by extra ozone addition. Capacitance drastically increased by temperature increase and ozone addition. Comparing with HfO 2 /Al 2 O 3 /HfO 2 , capacitance increase was about 25% higher. Moreover, leakage current was effectively suppressed especially at negative bias comparing with single ZrO 2 . We also checked the scalability in Tox.eq by reducing the thickness of ZrO 2 deposited at 280℃ as shown in Fig.10. From the criteria of 1fA/cell(±1.0V) in terms of leakage, Tox.eq of around 6.3Å could be obtained by lowering thickness down to 32Å. This data also mean that 45nm generation can be possible even at 1.4um high storage node from Fig.1. Temperature dependent leakage current did not show any significant degradation until 90℃(Fig.11). Fig.12 shows the solid “0” fail bit counts of ZAZ TIT capacitor applied to the currently mass produced 0.1um 512M DDR device. Fail bits are negligible up to 2.2V maintaining 10 bits or less in spite of low Tox.eq(9.9Å). ZAZ TIT capacitor turned out to be very reliable satisfying 10 year (10 5 hours at 0.7V operation) lifetime criteria as shown in Fig.13. We finally confirmed the mass production-wise reliability by packaging test as shown in Fig.14. There was no big difference in yield at each test items comparing with currently mass produced SIS Al 2 O 3 capacitor. Conclusion We have proposed a new ZAZ(ZrO 2 /Al 2 O 3 /ZrO 2 ) capacitor dielectric from crystalline ZrO 2 and amorphous Al 2 O 3 for the application to TIT capacitor. It was successfully demonstrated that newly designed ZAZ TIT capacitor had excellent package reliability in mass production level requiring final device package. Moreover, it was found that Tox.eq of ZAZ dielectric could be lowered to 6.3Å still using TiN electrode required for 45nm generation DRAM devices. References [1] D.S. Kil, et al., VLSI Tech. Dig., pp 73, 2004 [2] K.R. Yoon, et al., SSDM, pp 188, 2005 [3] Xinyuan Zhao et at., Physical Review B, 075105, Vol.65 1-4244-0005-8/06/$20.00 (c) 2006 IEEE 2006 Symposium on VLSI Technology Digest of Technical Papers