Composition and Growth Kinetics of the Interfacial Layer for MOCVD HfO[sub 2] Layers on Si Substrates

Abstract

To boost MOS transistor performance, thickness of the gate dielectric is continuously scaled down. This results in an increase of gate tunneling leakage current, which at some point prevents further downscaling. Desired parameters of alternative materials to SiO 2 are a higher dielectric constant ͑high-k materials͒, stability, and compatibility with silicon. A general observation for one of the prime candidates, HfO 2 , is formation of an interfacial layer between the silicon and the high-k material that limits scalability because of its low k-value. Hence, a thorough study of the formation of this layer and its contribution to the equivalent oxide thickness is of utmost importance. We studied the composition and growth kinetics of the interfacial layer formed during the deposition of HfO 2 by metallorganic chemical vapor deposition using O 2 and tetrakis-diethylamidohafnium as precursor. We found the composition and thickness of the interfacial layer to be dependent on the deposition parameters as well as on the starting surface. The layer's composition is hafnium silicate-like and its thickness increases as a function of deposition time and temperature. It is therefore controlled by deposition of the HfO 2 layer. SiO 2 has been used for decades as the gate isolator material in complementary metal-oxide semiconductor ͑CMOS͒ technology. Downscaling of the gate dielectric to improve device performance is reaching physical limits where the gate material consists of only a few atomic layers, resulting in unacceptably high leakage currents.1 Reducing the leakage current through nitridation prolongs the lifespan of SiO 2 , 2 but according to the International Technology Roadmap for Semiconductors ͑ITRS͒, industry will from 2005 on abandon SiO 2 as a gate material and start replacing it with materials having a higher dielectric constant ͑high-k materials͒. 3 The urgent need for these new materials has resulted in extensive research on several high-k candidates, such as Al 2 O 3 , ZrO 2 , HfO 2 , ZrSiO x , HfSiO x , etc. At present, Hf-based materials are the most likely candidates.Si and SiO 2 as a gate material are chemically perfectly compatible, which was, among others, one of the reasons for choosing Si and for the success of the silicon semiconductor industry. For high-k materials possible interactions between Si ͑both substrate and polySi electrode͒ and the high-k material are an additional concern needing to be addressed. For example, these interactions can result in silicide formation at the high-k/polysilicon interface, as has been observed for ZrO 2 . 4 In addition, there is also an important difference in processing; whereas SiO 2 as gate dielectric is grown simply by oxidation of the silicon substrate, high-k materials have to be deposited. Such deposition is not straightforward and it has been found that the deposition behavior of a high-k layer can be highly dependent upon the starting surface.5 Moreover, we have observed that metallorganic chemical vapor deposition ͑MOCVD͒ of HfO 2 on various starting s...

Study of CVD high-k gate oxides on high-mobility Ge and Ge/Si substrates

“…A more than likely explanation is that the grown Si-layer is not preserved during deposition. This is in agreement with earlier observations of Silicate formation for HfO 2 depositions on Si, demonstrating that during deposition intermixing occurs at the interface [9]. …”

“…Note that a reduced oxide growth cannot be attributed to a capping effect of HfO 2 because the layers are very thin (< 1.5 nm) and HfO 2 is not an oxygen barrier. On the contrary, for silicon HfO 2 has been observed to catalyze the oxidation resulting in a thicker interfacial layer [9].…”

HfO2 and Hf1–xSixO2 Thin Films Grown by Metal‐Organic CVD Using Tetrakis(diethylamido)hafnium

“…[15] A source that is both liquid and stable at room temperature can be obtained by substituting C 2 H 5 for CH 3 in the molecule, [15,16] and tetrakis(diethylamido)hafnium (Hf(N(C 2 H 5 ) 2 ) 4 ; H(NEt 2 ) 4 ) and tetrakis(ethylmethylamido)hafnium (Hf(N(C 2 H 5 )(CH 3 )) 4 ; H(NEtMe) 4 ) are considered as being novel precursors for metal-organic (MO)CVD. [17,[22][23][24][25][26][27][33][34][35][36][37] In this paper, we report on the properties of the Hf(NEt 2 ) 4 precursor and the deposited HfO 2 and Hf 1-x Si x O 2 films. When Hf 1-x Si x O 2 was deposited by LPCVD using Hf(NEt 2 ) 4 , the silicon source strongly affected the film's properties.…”

Effect of RF power of post-deposition oxygen treatment on HfO 2 gate dielectrics

“…In addition to a high dielectric constant, HfO 2 films have other advantages, such as a large band gap offset from that of Si and high thermal stability on silicon substrates [2][3][4][5]. Many methods for HfO 2 film deposition, such as sputtering, electron-beam evaporation, metal organic chemical vapor deposition, and atomic layer deposition (ALD), have recently been used [5][6][7][8].…”