XPS Analyses and Work Function Extraction of Titanium Nitride Electrodes for MOS Technology and Schoktty Diode.

摘要

Titanium nitride (TiN) films have been obtained by DC sputtering deposition in a nitrogen/argon ambient on Si substrates. TiN film have been used as gate electrodes in MOS capacitors, which were fabricated with SiO_2 as gate dielectric, and in Schoktty diodes on n-type Si (100) substrates. 20nm and 100nm thick TiN layers were deposited by DC sputtering in N_2:Ar (20:60 sccm) ambient, with a sputtering power of 1000 W. These films presented electrical resistivity of 300 μΩ.cm and poly crystalline strucure [1]. XPS analysis evidence TiN and TiO_xN_y formation in both 20 nm (Figure 1a) and 100 nm (Figure 1b) thick films. TiO_xN_y formation could be related with the exposure the metal electrode to air. To get MOS capacitors with TiN/SiO_2/Si/AI and AI/TiN/SiO_2/Si/AI structures, the Si substrates were used and were cleaned with a standard RCA method. After, dry thermal oxidation at 1000°C for 2 min was carried out and a 8 nm thick SiO_2 layer on Si was obtained. 20 nm and 100nm thick TiN layer was deposited on SiO_2/Si by DC sputtering. Finally, in some devices a 200nm thick alumininum (Al) layer was deposited on TiN layer by DC sputtering, in order to reduce the TiO_xN_y formation on the metal electrode. MOS capacitor pattern was defined by a mask composed of an array of 200 pm diameter dots. These devices were sintered in conventional furnace in forming gas at 450 °C for 30 minutes and were electrical characterized by capacitance-voltage (C-V) measurements. Figure 2 presents MOS capacitor C-V characteristics.TiN work function values and flat-band voltage were extracted from all C-V measurements using CVC software [2] and 1/C<@@>~2 method [3]. The extracted TiN work function values and flat-band voltage were between 4.0 and 4.3 eV, -0.17 and 0.36 V, respectively. These results agree with results presented on Reference [4]. The variations on work function values are related with the dipole variations due the interface between metal and dielectric. To investigate the TiN work function, Schoktty diodes were fabricated in the same substrate of MOS capacitors. Titanium nitride (TiN) layer were deposited by DC sputtering in a N_2:Ar (20:60 sccm) ambient, with a sputtering power of 1000 W. TiN/Si/AI and AI/TiN/Si/AI diodes were formed with TiN (20nm and 100nm) gate electrodes and Al layer (200nm) were deposited by DC sputtering process. These diodes were sintered in conventional furnace in forming gas at 450 °C for 30 minutes. The electrodes were patterned with a mask composed of an array of 200 μm diameter dots. These diodes were electrical characterized by current-voltage (I-V) measurements (Figure 3 and 4), and the ideality factor between 1.0 and 3.2, and work function values between 4.4 and 4.5 eV were extracted, which is near the work function values for mid-gap electrode application [4,5]. The TiN work function values extracted from MOS capacitors and Schottky diodes with Al/TiN/SiO_2/Si/Al and lI/TiN/Si/Al sctructures were slightly higher than the TiN work function values extracted from same devices with the TiN/SiO_2/Si/Al and TiN/Si/AI structures, indicating that the TiN work function values increases with a lower incorporation of TiO_xN_y on the surface of TiN films.