Analysis of x‐ray irradiation effect in high‐k gate dielectrics by time‐dependent photoemission spectroscopy using synchrotron radiation

Abstract

We have developed a method to precisely determine the band offsets for hafnium oxide (HfO 2 ), hafnium silicate (HfSiO) and nitrided hafnium silicate (HfSiON) films on Si by elimination of x-ray irradiation effects with time-dependent photoemission spectroscopy (PES) and x-ray absorption spectroscopy. The core-level PES spectra shift during PES measurements, which is explained as the dielectric films charging due to photoemission by the x-ray irradiation. For elimination of the x-ray irradiation effect on the determination of the band offsets, time-dependent photoemission spectroscopy was performed. The precisely determined valence band offsets for HfO 2 , HfSiO and HfSiON are 3.2, 3.4, and 1.9 eV, respectively. On the other hand, the conduction band offsets are almost the same values of about 1.3 eV. Thus, the elimination of x-ray irradiation effect enables to precisely determine the band offsets, leading to the accurate estimation of gate leakage current.

Complete band offset characterization of the HfO2/SiO2/Si stack using charge corrected x-ray photoelectron spectroscopy

“…13,14,16,20,21 These values agree well with the results from this work that were not charge corrected. By correcting for charging, we obtain HfO 2 -Si VBO values which are more in agreement with values measured using UPS and IPE, which range from 2.5 to 3.0 eV.…”

“…The CBOs we determined, which ranged from 1.59 to 2.12 eV, were well above the minimum CBO ͑1.0 eV͒, 18 which has been specified to be a requirement in order to achieve acceptable gate leakage current, and among the higher CBOs that have been reported. 10,11,[14][15][16][18][19][20][21][22]53 …”

“…6,9 The measurement of the band offsets in a HfO 2 / SiO 2 / Si stack has received much attention over the past decade because the band offsets are directly related to the gate leakage current for thin oxide stacks. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] The primary methods that have been used for this characterization are x-ray, soft x-ray, UV, and inverse photoelectron spectroscopies ͑XPS, SXPS, UPS, and IPS, respectively͒, internal photoemission ͑IPE͒, and ballistic electron energy spectroscopy ͑BEES͒. The reported values for the HfO 2 -Si valence band offset ͑VBO͒ span a range from 2.5 to 3.4 eV.…”

“…13,14,16,20,21 These XPS based measurements of the HfO 2 -Si VBO did not, however, take the effect of sample charging into account. In this study, we have measured the HfO 2 -Si VBO while taking sample charging into account, and have obtained values that are in closer agreement with those on the lower end of the range of published VBO values.…”

Study of Direct-Contact HfO2/Si Interfaces

“…This means that both conduction band offset ( Φ s ) at the HfO 2 /Si interface and HfO 2 thickness govern electron tunneling. Since the conduction band offset of the SiO 2 /Si interface ( Φ s ~3.15 eV) [ 34 ] is larger than that of the HfO 2 /Si interface ( Φ s ~1.1–1.5 eV) [ 35 , 36 , 37 ], the leakage current is expected to decrease by inserting an Si oxide layer, as indicated by the dotted line in Figure 4 . However, the J g of HfO 2 /TG-SiO 2 /Si MOS capacitors increases once and then decreases, probably meaning that the barrier height is reduced by the insertion of an interface Si oxide.…”