Interfacial Reaction in Poly Si 1 Àx Ge x Õ ZrO 2 with Ge Content in Poly Si 1 Àx Ge x Films S. K. Kang, a, * B. G. Min, a J. H. Yoo, a S. W. Nam, a D.-H. Ko, a,z H. B. Kang, b C. W. Yang, b and M.-H. Cho c a Department of Ceramic Engineering, Yonsei University, Seoul, Korea b School of Metallurgy and Material Engineering, Sung Kyun Kwan University, Suwon, Korea c School of Materials Science and Engineering, Stanford University, Stanford, California, USA The interfacial reaction between poly Si 1-x Ge x ( x = 0, 0.2, 0.4) and ZrO 2 films after annealing was investigated to use ZrO 2 films as an alternative gate dielectric. In the poly Si/ZrO 2 structure, silicidation was the dominant reaction due to continuous formation of Zr-silicide and SiO during annealing. However, in poly Si 1-x Ge x ( x = 0.2, 0.4)/ZrO 2 , silicate formation was the main reaction after annealing at 900°C for 30 min. In addition, after annealing at 800°C, the silicate layer was observed only in the poly Si 0.6 Ge 0.4 /ZrO 2 system. © 2002 The Electrochemical Society. DOI: 10.1149/1.1516907 All rights reserved. Manuscript submitted June 20, 2002; revised manuscript received August 21, 2002. Available electronicallyOctober 9, 2002. As the size of complementary metal oxide semiconductor CMOS technology devices scales down, studies on replacing the currently employed SiO 2 with high-k dielectrics have received con- siderable attention since conventional SiO 2 shows serious problems, such as the increase of leakage current and the degradation of reli- ability in the sub-0.1 m process. 1,2 Several high-k dielectric mate- rials have been investigated as an alternative gate dielectric, 3-6 how- ever, their application is limited due to the interfacial reaction between high-k materials and the gate electrode or Si substrate dur- ing the post process. Among suggested materials, ZrO 2 films have many advantages, such as a high dielectric constant 15-22 and a relatively large bandgap 5.2-7.8 eV. 4,5 Besides these advantages, high-k dielectric films must be thermally stable with the gate elec- trode during the post process for compatibility with conventional processes. From the thermodynamic data, ZrO 2 is expected to be stable with poly Si gate electrode during the post process. However, several electrical results of CMOS field-effect transistor FET with poly Si/ZrO 2 gate structure showed some issues, such as high leak- age current and low capacitance due to the silicidation between poly Si and ZrO 2 . 7,8 Therefore, prevention of silicidation between the poly Si gate electrode and ZrO 2 films was important during the post process. Although the insertion of barrier material between poly Si and ZrO 2 films is suggested to prevent degradation of electrical properties, that process causes complexity and incompatibility with conventional processes. In this paper, poly Si 1-x Ge x films were used as a gate electrode to prevent silicidation during the post process. It is well known that Ge in epi Si 1-x Ge x films retarded silicidation in the Ti, Co, Zr/Si 1-x Ge x system as compared to the Co, Ti, Zr/Si system. 9-11 From these previous results, compared with the poly Si/ZrO 2 sys- tem, silicidation is retarded in the poly Si 1-x Ge x /ZrO 2 system and then retardation of silicidation is expected to bring about another reaction, silicate formation in poly Si 1-x Ge x /ZrO 2 . Although the formation of a thin silicate layer lowers capacitance of the gate oxide, interfacial properties are enhanced and leakage current is de- creased. In addition, poly Si 1-x Ge x films have been suggested as a promising alternative to the currently employed poly Si gate elec- trode for CMOS-FETs due to suppression of B penetration and gate depletion. Experimental After standard cleaning of p-type silicon wafers, 5.8 nm thick ZrO 2 films were deposited at room temperature by reactive dc mag- netron sputtering from a Zr target with 99.9% purity in an Ar + O 2 gas ambient and 10 nm thick poly Si 1-x Ge x films ( x = 0, 0.2, 0.4) were grown on ZrO 2 films at 600°C using low pressure chemical vapor deposition LPCVD. After the formation of a metal oxide semiconductor structure, the specimens were an- nealed at 800 and 900°C in a N 2 ambient. Then, the interfacial reaction between poly Si 1-x Ge x and ZrO 2 films was investigated using X-ray photoelectron spectroscopy XPS. For XPS data acqui- sition, Al K radiation 1486.6 eV was used as photon source and the analysis chamber was maintained at 5  10 -9 Torr. All experi- mental scans were performed at a constant pass energy of 23.5 eV and a constant take-off angle of 45°. In addition, the XPS spectra were all taken at room temperature before and after Ar ion sputter- ing. Ar ion sputtering conditions were ion energy of 3 keV and beam current density of 1.5  10 -5 A/cm 2 . Results and Discussion Figure 1 shows Si 2p spectra of poly Si 1-x Ge x /ZrO 2 system after annealing at 900°C for 30 min. Initially, 10 nm poly Si 1-x Ge x films were etched to the poly Si 1-x Ge x /ZrO 2 interface by Ar ion sputtering in an XPS chamber and then the spectra of Zr 3d, O 1s, Si 2p, and Ge 2p were obtained at each sputtering step from the poly Si 1-x Ge x /ZrO 2 interface to the Si substrate. In poly Si/ZrO 2 films, the binding state of SiO x was weakly observed at the poly Si/ZrO 2 interface and that of pure Si or Si in silicide was observed at the poly Si/ZrO 2 interface. Because the peak position of Si 2p in silicide is similar to that of pure Si, it is difficult to identify the binding states of Si. From the Zr spectra, the binding state of Si at the poly Si/ZrO 2 interface is expected to be silicide Fig. 2. We discuss the formation of Zr silicide and SiO x in the latter thermodynamic con- siderations. In contrast to the poly Si/ZrO 2 system, notable features were shown in the poly Si 0.8 Ge 0.2 /ZrO 2 and poly Si 0.6 Ge 0.4 /ZrO 2 films. The peak intensity of binding states of SiO x increased clearly at a binding energy of about 103 eV and that of silicide diminished at about 99.3 eV. In addition, the peak intensity of binding states of SiO x increased with the increase of Ge content in poly Si 1-x Ge x films. From the spectra of Si 2p, the formation of the silicate layer is dominant at the poly Si 1-x Ge x ( x = 0.2, 0.4)/ZrO 2 interface. The formation of a silicide layer at the poly Si/ZrO 2 interface and that of a silicate layer at the poly Si 1-x Ge x /ZrO 2 interface were confirmed from the Zr 3d spectra, as shown in Fig. 2. In poly Si/ZrO 2 film, the peaks of binding energy, about 179 and 183.3 eV, were observed at the poly Si/ZrO 2 interface. The peak at a binding energy of about 183.3 eV is the spectra of ZrO 2 and that of about 179 eV is expected to be the spectra of Zr in Zr-silicide or etched Zr; these peak positions are similar. Etched Zr may be ob- * Electrochemical Society Student Member. z E-mail: dhko@yonsei.ac.kr Electrochemical and Solid-State Letters, 5 12 G113-G115 2002 0013-4651/2002/512/G113/3/$7.00 © The Electrochemical Society, Inc. G113