硅基高κ材料的分子束外延生长
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摘要
在过去二十多年里,Si基元器件的大小遵循Moore定律按比例的持续减小。对于下一代金属氧化物半导体场效应管(MOSFET)器件,原来的栅极介电材料SiO_2已经不再适合使用。人们需要寻找适合的高k(k指介电常数)材料作为MOSFET器件中新的栅极材料。这其中,有两类材料最受关注。其中之一是IVB族金属氧化物,包括HfO_2和ZrO_2;另一类是ⅢA和ⅢB族氧化物,包括Al_2O_3和Y_2O_3,CeO_2等其他一些稀土金属氧化物。在这篇论文里,我们主要研究高k氧化物HfO_2和Er_2O_3的生长及其特性。
第一、二章将分别介绍研究背景和实验仪器。
在第三章中,我们将研究HfO_2的生长及其基本的物理和化学性质。HfO_2薄膜由电子束蒸发法获得。X射线光电子能谱(XPS)研究证明薄膜是符合化学剂量比的。透射电子显微镜(TEM)结果显示薄膜呈多晶状。原子力显微镜(AFM)结果表明薄膜表面非常平整,无空洞。对12nm厚的HfO_2而言,其均方根粗糙度为0.16nm。由电学方法得出薄膜总的介电常数为18。
第四章主要研究了以下四个方面。第一,Si基HfO_2薄膜的热稳定性。对在900℃和一个大气压的N_2气氛下快速退火30s的HfO_2薄膜,扫描电子显微镜(SEM)和AFM结果发现薄膜表面依然很平整,无空洞。这表明在这种条件下薄膜未发生分解反应,其热稳定性良好。但是,同步辐射光电子能谱研究表明在超高真空条件下HfO_2薄膜在温度为750℃时开始分解。第二,HfO_2薄膜与Si的能带偏差。基于光电子能谱的方法用于研究HfO_2薄膜与Si的价带偏差,其值约为3.46eV。第三,HfO_2薄膜的禁带宽度。从01s的能量损失谱上可获得HfO_2的禁带宽度值约为5.0ev。第四,我们采用在位的光电子能谱方法研究HfO_2薄膜的初期生长。实验观察到,即使对非常薄的HfO_2薄膜,界面处存在富Si的硅酸盐(silicate)层。这层界面层的形成与Hf可能促进氧化的作用有关。
第五章中主要论述Er_2O_3薄膜在Si(001)和Si(111)上的外延生长,也包括Si衬底表面的薄SiO_2层对Er_2O_2外延生长的影响。Er_2O_3薄膜和Si的外延关系由XRD和RHEED来确定。在Si(001)衬底上,其外延关系为Er_2O_3(110)//Si(001),Er_2O_3[001]//Si[110]或Er_2O_3[110]//Si[110]。在Si(111)衬底上,其外延关系为Er_2O_3(111)//Si(111)。在较低的生长气压或/和较低的生长温度下,Er的硅
For continued technology scaling, high k materials are required to replace SiO_2 as gate dielectric in the next generation metal oxide field effect transistors (MOSFET). Two kinds of materials are most promising. One is Group IVB metal oxides such as HfO_2 and ZrO_2; the other is Group IIIA and Group IIIB metal oxides including Al_2O_3, Y_2O_3 and some other rare earth oxides. In this thesis, we have studied the growth and characterization of high k materials HfO_2 and Er_2O_3.Here, the first two chapters introduce the research background and experimental equipments.In Chapter 3, the MBE growth and characterization of HfO_2 films are discussed. HfO_2 films were grown by electron beam evaporation using a metallic Hf source. Firstly, the basic physical and chemical properties of the as-grown films were characterized by using the corresponding methods. The as-deposited films are stoichiometric and polycrystalline, as verified by X-ray spectroscopy (XPS) and transmission electron microscopy (TEM) results, respectively. Atomic force microscopy (AFM) images show an extremely smooth surface obtained, with a root-mean-square (rms) roughness of about 0.16 nm for a 12 nm thick HfO_2 film. The films exhibit the overall dielectric constant of 18.Chapter 4 includes the following four sections. Firstly, the thermal stability of HfO_2 films on Si substrates. For the HfO_2 films upon rapid temperature annealing (RTA) at 900℃ in 1 atm N_2 for 30 s, both scan electron microscopy (SEM) and AFM results show a flat surface, and no voids or pits are found, indicating a good thermal stability of HfO_2 films upon annealing in the N_2 ambient. However, HfO_2 films begin to decompose at about 750℃ under the ultrahigh vacuum (UHV) condition, as verified by synchrotron radiation photoemission spectroscopy (SRPES) results. Secondly, band offset of HfO_2 films on Si(001). The photoemission based method proposed by Kraut et al. is used to determine the band offset of HfO_2 with Si. Accordingly, the valence band offset of HfO_2 with Si is 3.46 eV. Thirdly, the band gap of HfO_2. By using the O 1s energy loss spectrum, the band gap of HfO_2 films is roughly measured to be about 5.0 eV. The relatively small value obtained mainly arises from the lower energy resolution due to the non-monochromatic Mg ka x-ray used. The last section concerns in situ photoemission study on initial growth of HfO_2 films on Si(001) is also included in Chapter 4. Interfacial layers between HfO_2 and the Si substrate are observed even for very thin HfO_2 films and confirmed to be Si-rich
第一、二章将分别介绍研究背景和实验仪器。
在第三章中,我们将研究HfO_2的生长及其基本的物理和化学性质。HfO_2薄膜由电子束蒸发法获得。X射线光电子能谱(XPS)研究证明薄膜是符合化学剂量比的。透射电子显微镜(TEM)结果显示薄膜呈多晶状。原子力显微镜(AFM)结果表明薄膜表面非常平整,无空洞。对12nm厚的HfO_2而言,其均方根粗糙度为0.16nm。由电学方法得出薄膜总的介电常数为18。
第四章主要研究了以下四个方面。第一,Si基HfO_2薄膜的热稳定性。对在900℃和一个大气压的N_2气氛下快速退火30s的HfO_2薄膜,扫描电子显微镜(SEM)和AFM结果发现薄膜表面依然很平整,无空洞。这表明在这种条件下薄膜未发生分解反应,其热稳定性良好。但是,同步辐射光电子能谱研究表明在超高真空条件下HfO_2薄膜在温度为750℃时开始分解。第二,HfO_2薄膜与Si的能带偏差。基于光电子能谱的方法用于研究HfO_2薄膜与Si的价带偏差,其值约为3.46eV。第三,HfO_2薄膜的禁带宽度。从01s的能量损失谱上可获得HfO_2的禁带宽度值约为5.0ev。第四,我们采用在位的光电子能谱方法研究HfO_2薄膜的初期生长。实验观察到,即使对非常薄的HfO_2薄膜,界面处存在富Si的硅酸盐(silicate)层。这层界面层的形成与Hf可能促进氧化的作用有关。
第五章中主要论述Er_2O_3薄膜在Si(001)和Si(111)上的外延生长,也包括Si衬底表面的薄SiO_2层对Er_2O_2外延生长的影响。Er_2O_3薄膜和Si的外延关系由XRD和RHEED来确定。在Si(001)衬底上,其外延关系为Er_2O_3(110)//Si(001),Er_2O_3[001]//Si[110]或Er_2O_3[110]//Si[110]。在Si(111)衬底上,其外延关系为Er_2O_3(111)//Si(111)。在较低的生长气压或/和较低的生长温度下,Er的硅
For continued technology scaling, high k materials are required to replace SiO_2 as gate dielectric in the next generation metal oxide field effect transistors (MOSFET). Two kinds of materials are most promising. One is Group IVB metal oxides such as HfO_2 and ZrO_2; the other is Group IIIA and Group IIIB metal oxides including Al_2O_3, Y_2O_3 and some other rare earth oxides. In this thesis, we have studied the growth and characterization of high k materials HfO_2 and Er_2O_3.Here, the first two chapters introduce the research background and experimental equipments.In Chapter 3, the MBE growth and characterization of HfO_2 films are discussed. HfO_2 films were grown by electron beam evaporation using a metallic Hf source. Firstly, the basic physical and chemical properties of the as-grown films were characterized by using the corresponding methods. The as-deposited films are stoichiometric and polycrystalline, as verified by X-ray spectroscopy (XPS) and transmission electron microscopy (TEM) results, respectively. Atomic force microscopy (AFM) images show an extremely smooth surface obtained, with a root-mean-square (rms) roughness of about 0.16 nm for a 12 nm thick HfO_2 film. The films exhibit the overall dielectric constant of 18.Chapter 4 includes the following four sections. Firstly, the thermal stability of HfO_2 films on Si substrates. For the HfO_2 films upon rapid temperature annealing (RTA) at 900℃ in 1 atm N_2 for 30 s, both scan electron microscopy (SEM) and AFM results show a flat surface, and no voids or pits are found, indicating a good thermal stability of HfO_2 films upon annealing in the N_2 ambient. However, HfO_2 films begin to decompose at about 750℃ under the ultrahigh vacuum (UHV) condition, as verified by synchrotron radiation photoemission spectroscopy (SRPES) results. Secondly, band offset of HfO_2 films on Si(001). The photoemission based method proposed by Kraut et al. is used to determine the band offset of HfO_2 with Si. Accordingly, the valence band offset of HfO_2 with Si is 3.46 eV. Thirdly, the band gap of HfO_2. By using the O 1s energy loss spectrum, the band gap of HfO_2 films is roughly measured to be about 5.0 eV. The relatively small value obtained mainly arises from the lower energy resolution due to the non-monochromatic Mg ka x-ray used. The last section concerns in situ photoemission study on initial growth of HfO_2 films on Si(001) is also included in Chapter 4. Interfacial layers between HfO_2 and the Si substrate are observed even for very thin HfO_2 films and confirmed to be Si-rich
引文
1. N. Tsuda, K. Nasu, A. Yanase and K. Siratori, Electronic Conduction in Oxides, Springer-Verlag, Berlin, 1991.
2. D. P. Norton, Mat. Sci. Eng. R 43, 139(2004)
3. E. J. Tarsa, K. L. McCormick and J. S. Speck, Mat. Res. Soc. Symp. Pro. 341, 73(1994)
4. R. H. Dennare et al., IEEE J. Solid state Circuits Sc-9, 256(1974)
5. G. Baccarani et al., IEEE Trans. Electron Dev. Ed-31, 452(1984)
6. M. Cao, P. V. Voorde, M. Cox and W. Greene, IEEE Electron Device Lett. 19, 291(1998)
7. G. D. Wilk, R. M. Wallace and J. M. Anthoy, J. Appl. Phys. 89, 5243(2001)
8. S. M. Sze, Physics of Semiconductor Devices, 2nd ed. Wiley, New York, 1981.
9. http://public.itrs.net
10. J. Robertson, J. Vac. Sci. Technol. B 18, 1785(2000)
11. R. M. C. de Almeida and I. J. R. Baumvol, Surf. Sci. Rep. 49, 1(2003)
12. R. M. Wallace, Appl. Surf. Sci. 231-232, 543(2004)
13. D. Barlage et al., (Intel) IEDM 231(2001)
14. W.Zhu et al., IEDM 463(2001)
15. H. -J. Cho, C. S. Kang, K. Onishi, S. Gopalan, R. Nieh, R. Choi, E. Dharmarajan and J. C. Lee, IEDM 30(2001)
16. R. A. McKee, F. J. Walker, and M. F. Chisholm, Phys. Rev. Lett. 81, 3014(1998)
17. S. A. Chambers, Surf. Sci. Rep. 39, 105(2000)
18. T. S. Kalkur and Y. C. Lu, Thin Solid Films 188, 203(1990)
19. V. Mikhelashvili, G. Eisenstein, F. Edelman, R. Brener, N. Zakharov and P. Werner, J. Appl. Phys. 95, 613(2004)
20. V. Mikhelashvili, G. Eisenstein and F. Edelman, Appl. Phys. Lett. 80, 2156(2002)
21. M. P. Singh, C. S. Thakur, K. Shalini, N. Bhat and S. A. Shivashankar, Appl. Phys. Letter. 83, 2889(2003)
22. L. Esaki and R. Tsu, IBM J. Res. Dev. 14, 61(1970)
23. R. Tsu, Nature 364, 364(1993)
24 Z. H. Lu, D. J. Lockwood and J. -M. Baribeau, Naure 378, 258(1995)
2. D. P. Norton, Mat. Sci. Eng. R 43, 139(2004)
3. E. J. Tarsa, K. L. McCormick and J. S. Speck, Mat. Res. Soc. Symp. Pro. 341, 73(1994)
4. R. H. Dennare et al., IEEE J. Solid state Circuits Sc-9, 256(1974)
5. G. Baccarani et al., IEEE Trans. Electron Dev. Ed-31, 452(1984)
6. M. Cao, P. V. Voorde, M. Cox and W. Greene, IEEE Electron Device Lett. 19, 291(1998)
7. G. D. Wilk, R. M. Wallace and J. M. Anthoy, J. Appl. Phys. 89, 5243(2001)
8. S. M. Sze, Physics of Semiconductor Devices, 2nd ed. Wiley, New York, 1981.
9. http://public.itrs.net
10. J. Robertson, J. Vac. Sci. Technol. B 18, 1785(2000)
11. R. M. C. de Almeida and I. J. R. Baumvol, Surf. Sci. Rep. 49, 1(2003)
12. R. M. Wallace, Appl. Surf. Sci. 231-232, 543(2004)
13. D. Barlage et al., (Intel) IEDM 231(2001)
14. W.Zhu et al., IEDM 463(2001)
15. H. -J. Cho, C. S. Kang, K. Onishi, S. Gopalan, R. Nieh, R. Choi, E. Dharmarajan and J. C. Lee, IEDM 30(2001)
16. R. A. McKee, F. J. Walker, and M. F. Chisholm, Phys. Rev. Lett. 81, 3014(1998)
17. S. A. Chambers, Surf. Sci. Rep. 39, 105(2000)
18. T. S. Kalkur and Y. C. Lu, Thin Solid Films 188, 203(1990)
19. V. Mikhelashvili, G. Eisenstein, F. Edelman, R. Brener, N. Zakharov and P. Werner, J. Appl. Phys. 95, 613(2004)
20. V. Mikhelashvili, G. Eisenstein and F. Edelman, Appl. Phys. Lett. 80, 2156(2002)
21. M. P. Singh, C. S. Thakur, K. Shalini, N. Bhat and S. A. Shivashankar, Appl. Phys. Letter. 83, 2889(2003)
22. L. Esaki and R. Tsu, IBM J. Res. Dev. 14, 61(1970)
23. R. Tsu, Nature 364, 364(1993)
24 Z. H. Lu, D. J. Lockwood and J. -M. Baribeau, Naure 378, 258(1995)