Applications of W-based thin films for semiconductor device fabrication
Tungsten(W) is applied to the current semiconductor devices such as W-plug process, metal gate of 3D NAND flash, or bit line of DRAM, due to its extremely low bulk resistivity. Additionally, some thin films of other tun...
Applications of W-based thin films for semiconductor device fabrication
Tungsten(W) is applied to the current semiconductor devices such as W-plug process, metal gate of 3D NAND flash, or bit line of DRAM, due to its extremely low bulk resistivity. Additionally, some thin films of other tungsten compounds such as WNx, WCx, and WNxCy also have an important role in the current semiconductor devices applications such as diffusion barrier, metallization, hard coating, solid lubricant, catalyst, superconductors, sensors, channel layers, etc. Among these tungsten compounds, tungsten nitrides (WNx) thin films have been studied due to their high thermal and chemical stabilities with high resistance to diffusion of foreign atoms, controllable work function, melting temperature and low resistivity.[1][2][3][4] Furthermore, Tungsten nitride has two stable phases hexagonal tungsten mono nitride(WN) and tungsten di nitride(W2N), which are well known for the better properties of resistivity and diffusion barrier properties in the W2N phase.[5] As these properties, tungsten nitride, especially, have been studied for various applications, including the diffusion barrier layer for metallization, contact / glue layer for W-plug, electrode, catalyst for oxygen evolution reaction etc.[1][5][6][7][8] So far, WNx films have been deposited using various physical vapor deposition (PVD), and chemical vapor deposition (CVD) methods[1-4]. As increasing the N2 gas flow rate in a gas mixture of W target in the mixture plasma of Ar and N2, in the case of sputtering of PVD, the phase was transformed from W to WNx. Furthermore, as the rate of N2 in the film increased, the difference was not only diffusion barrier performance but also resistance was affected.[2] The other is CVD or plasma enhanced CVD (PECVD)-WNx processes which using the chemical reaction between W-precursor and reactant including the nitrogen source. In this case, there is two major types of the W-precursors of metal-organic precursors such as W(CO)6 [9] and bis (tertbutylimido)-bis(tertbutylamido) tungsten [TBIDMW, (tBuN)2(Me2N)2W [10][11], and the other is inorganic precursors such as WF6 [12][13]. All of these studies successfully deposited various WNx films, however, these methods have limitations on the properties of films such as uniformity of film thickness over a large surface and conformality in extremely narrow and complex (high aspect ratio) architectures. To overcome these disadvantages of properties of WNx thin film, here, atomic layer deposition (ALD) seems to be the best option to prepare any thin film which would find its suitability in future technology with precise controllability of a film thickness, conformality, and almost perfect large-area uniformity due to its surface-saturated and self-limited reaction mechanism.[14][15] So far, many studies of the ALD of WNx thin films were performed using WF6[5][16] [17] and metal-organic W precursor such as W2(NMe2)6[18], (tBuN)2(Me2N)2W[19], and W(CO)6[20] and NH3 molecule reactants. However, many case of using WF6 and metal-organic W precursor, the resistivity and growth rate relatively was high (~ 4500 μΩ-cm) and low (~ 0.042nm/cycle)[16]. Furthermore, the use of F-containing inorganic W precursor (WF6) precursor, has another critical issue due to the highly corrosive and toxic properties of the F and by-products such as HF resulting in etching of underlying materials and F impurities remaining on the surface impede the adhesion between WNx and Cu.[21] Therefore, WF6 and metal-organic based WNx thin film process has obvious limitations and study on using F-free W precursor and plasma reactant is required.
On the other hand, copper have been used as interconnection metal with low bulk resistivity of 1.7 μΩ-cm. However, Cu has disadvantages of diffusion into SiO2 layers or Si substrates at elevated temperatures during semiconductor device fabrication and forms the copper silicide which increase the total resistivity at the interface.[22][23] Therefore, diffusion barrier is required between Si substrate or SiO2 and interconnection metal to prevent the diffusion of Cu. Furthermore, in the case of using Cu as interconnect metal, the size effect which increases the device resistivity due to electron surfaces and grain boundary scattering considered to challenges in recent continuous downscaling of device width and pitch (less than Cu electron mean free path, Cu 39 nm). In this regards, to overcome the size effects, Ru with low bulk resistivity (~ 7.1 μΩ-cm), short electron mean free path (~ 6.6 nm) and high thermal stability is considered as one of the candidates of Cu.[24][23][25] And also, as the size of semiconductor devices has become extremely narrow(in few nm), it has become difficult to deposit a thin film with a precise thickness in a complex structure. Therefore, ALD method to deposit the extremely thin film is recommended.
In this study, we performed the plasma-enhanced WNx thin film using less corrosive by-products fluorine-free W precursor, WCl5, and various plasma reactants to reduce the resistivity and improve the growth rate. Deposited PEALD-WNx showed the typical ALD growth kinetic and also we confirmed the properties of WNx film including the crystallographic nature, elemental compositions, and the microstructures by controlling the ratio of N2 + H2 gas using several ex-situ characterization tools. Finally, ultrathin (~ 4 nm) PEALD-WNx films were successfully evaluated as a diffusion barrier against Cu and Ru.
Applications of W-based thin films for semiconductor device fabrication
Tungsten(W) is applied to the current semiconductor devices such as W-plug process, metal gate of 3D NAND flash, or bit line of DRAM, due to its extremely low bulk resistivity. Additionally, some thin films of other tungsten compounds such as WNx, WCx, and WNxCy also have an important role in the current semiconductor devices applications such as diffusion barrier, metallization, hard coating, solid lubricant, catalyst, superconductors, sensors, channel layers, etc. Among these tungsten compounds, tungsten nitrides (WNx) thin films have been studied due to their high thermal and chemical stabilities with high resistance to diffusion of foreign atoms, controllable work function, melting temperature and low resistivity.[1][2][3][4] Furthermore, Tungsten nitride has two stable phases hexagonal tungsten mono nitride(WN) and tungsten di nitride(W2N), which are well known for the better properties of resistivity and diffusion barrier properties in the W2N phase.[5] As these properties, tungsten nitride, especially, have been studied for various applications, including the diffusion barrier layer for metallization, contact / glue layer for W-plug, electrode, catalyst for oxygen evolution reaction etc.[1][5][6][7][8] So far, WNx films have been deposited using various physical vapor deposition (PVD), and chemical vapor deposition (CVD) methods[1-4]. As increasing the N2 gas flow rate in a gas mixture of W target in the mixture plasma of Ar and N2, in the case of sputtering of PVD, the phase was transformed from W to WNx. Furthermore, as the rate of N2 in the film increased, the difference was not only diffusion barrier performance but also resistance was affected.[2] The other is CVD or plasma enhanced CVD (PECVD)-WNx processes which using the chemical reaction between W-precursor and reactant including the nitrogen source. In this case, there is two major types of the W-precursors of metal-organic precursors such as W(CO)6 [9] and bis (tertbutylimido)-bis(tertbutylamido) tungsten [TBIDMW, (tBuN)2(Me2N)2W [10][11], and the other is inorganic precursors such as WF6 [12][13]. All of these studies successfully deposited various WNx films, however, these methods have limitations on the properties of films such as uniformity of film thickness over a large surface and conformality in extremely narrow and complex (high aspect ratio) architectures. To overcome these disadvantages of properties of WNx thin film, here, atomic layer deposition (ALD) seems to be the best option to prepare any thin film which would find its suitability in future technology with precise controllability of a film thickness, conformality, and almost perfect large-area uniformity due to its surface-saturated and self-limited reaction mechanism.[14][15] So far, many studies of the ALD of WNx thin films were performed using WF6[5][16] [17] and metal-organic W precursor such as W2(NMe2)6[18], (tBuN)2(Me2N)2W[19], and W(CO)6[20] and NH3 molecule reactants. However, many case of using WF6 and metal-organic W precursor, the resistivity and growth rate relatively was high (~ 4500 μΩ-cm) and low (~ 0.042nm/cycle)[16]. Furthermore, the use of F-containing inorganic W precursor (WF6) precursor, has another critical issue due to the highly corrosive and toxic properties of the F and by-products such as HF resulting in etching of underlying materials and F impurities remaining on the surface impede the adhesion between WNx and Cu.[21] Therefore, WF6 and metal-organic based WNx thin film process has obvious limitations and study on using F-free W precursor and plasma reactant is required.
On the other hand, copper have been used as interconnection metal with low bulk resistivity of 1.7 μΩ-cm. However, Cu has disadvantages of diffusion into SiO2 layers or Si substrates at elevated temperatures during semiconductor device fabrication and forms the copper silicide which increase the total resistivity at the interface.[22][23] Therefore, diffusion barrier is required between Si substrate or SiO2 and interconnection metal to prevent the diffusion of Cu. Furthermore, in the case of using Cu as interconnect metal, the size effect which increases the device resistivity due to electron surfaces and grain boundary scattering considered to challenges in recent continuous downscaling of device width and pitch (less than Cu electron mean free path, Cu 39 nm). In this regards, to overcome the size effects, Ru with low bulk resistivity (~ 7.1 μΩ-cm), short electron mean free path (~ 6.6 nm) and high thermal stability is considered as one of the candidates of Cu.[24][23][25] And also, as the size of semiconductor devices has become extremely narrow(in few nm), it has become difficult to deposit a thin film with a precise thickness in a complex structure. Therefore, ALD method to deposit the extremely thin film is recommended.
In this study, we performed the plasma-enhanced WNx thin film using less corrosive by-products fluorine-free W precursor, WCl5, and various plasma reactants to reduce the resistivity and improve the growth rate. Deposited PEALD-WNx showed the typical ALD growth kinetic and also we confirmed the properties of WNx film including the crystallographic nature, elemental compositions, and the microstructures by controlling the ratio of N2 + H2 gas using several ex-situ characterization tools. Finally, ultrathin (~ 4 nm) PEALD-WNx films were successfully evaluated as a diffusion barrier against Cu and Ru.
주제어
#plasma atomic layer deposition WNx W2N WCl5 fluorine free W precursor Cu and Ru-diffusion barrier
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