We succeeded in growing Ge homoepitaxial films by metal–organic chemical vapor deposition (MOCVD) using tertiarybutylgermane (t-C4H9GeH3). We synthesized and investigated the characteristics of t-C4H9GeH3. The vapor pressure was sufficiently high in the CVD process. The precursor was sufficiently safe as it did not have a pyrophoric and explosive nature. The Ge homoepitaxial growth was achieved at 360 °C under reduced pressure on an appropriately cleaned Ge(001) substrate.
Ge homoepitaxial films are grown at low growth temperature of 320°C by metal-organic chemical vapor deposition (MOCVD) using tertiarybutylgermane (t-C4H9GeH3). We also performed ab initio calculations in order to reveal the chemical reaction for the epitaxial growth. As the result, it was revealed that the t-C4H9GeH3 was most likely decomposed into germane (GeH4) and isobutene [CH2=C(CH3)2] through the β-hydrogen elimination. We considered that this chemical nature allowed the growth temperature as low as that obtained by GeH4 precursor with sufficiently suppressed C impurity incorporation.
Currently, it is expected that Ru is going to be introduced in place of Cu, which is the mainstream interconnect material in the very large scale integrated (VLSI) circuit. As high integration has been proceeding, the interconnect is expected not only having excellent electrical characteristics and reliability, but also providing an effective pathway for the removal of the heat generated by device operation [1]. The increasing current density in the narrowing interconnect produces Joule heat. The generated heat is removed by a heat sink attached to the substrate through the interconnect. Therefore, if the thermal resistance between the substrate and the interconnect is high, the heat cannot be removed efficiently and the interconnect temperature rises, lead to a degradation of VLSI reliability [2].
Recent work on the research of layered materials has revealed the material’s unique physical properties, its applications in various fields, and fabrication processes to produce high quality samples. We have been focusing on transition metal dichalcogenides (TMD) and its alloys. Fabrication of TMD alloys enables bandgap/band offset tuning which expands the application of TMD materials in various fields to a further extent. Although it has been predicted the fabrication of TMD alloys is difficult since the alloys are expected to be thermodynamically unstable [1,2], we have so far fabricated metal alloy, Mo 1- x W x S 2 [3], and chalcogen alloy, MoS 2(1- x ) Te 2 x [4]. In these studies, we have confirmed the control of composition by adjusting sputtering condition as well as bandgap and band offset shift according to the composition. However, the stability of the material, especially the change of physical properties over certain period of time, has not been discussed in depth despite the fact that such alloy material are thermodynamically unstable, as mentioned above. In addition, although there are numerous results on the fabrication differences, there are not many reports discussing on the stability of the fabricated films for TMDs [5]. In this study, we focused on the stability of the materials and optimization of fabrication condition in order to prevent degradation. MoS 2(1- x ) Te 2 x alloys are fabricated by co-sputtering MoS 2 and MoTe 2 followed by tellurization by inorganic Te precursor, (i-C 3 H 7 ) 2 Te, in H 2 or N 2 ambient. The samples were stored in a vacuum dessicator for a period of time (which we will refer as “storage time”) and then evaluated with X-ray photoelectron spectroscopy (XPS). It was revealed that depending on the carrier gas, or the ambient, during tellurization, the amount by which Mo is oxidized after the storage time is different despite the fact that the samples showed almost identical chemical state right after the tellurization. This may be attributed to the difference in grain size where H 2 ambient may have produced films with smaller grain size, i.e. longer or more grain boundaries, resulting in more area to be oxidized compared to N 2 ambient. This work was partly supported by JST CREST Number JPMJCR16F4, Japan. This work was also partly supported by JSPS KAKENHI Grant Number 18F22879 and 16J11377. Reference H. P. Komsa, et al. , J. Phys. Chem. Lett. 3 , 3652 (2012) J. Kang, et al. , J. Appl. Phys. 113 , 143703 (2013) Y. Hibino, et al. , Jpn. J. Appl. Phys. 57 , 06HB04 (2018) Y. Hibino, et al. , J. Mater. Res. 32 , 3021 (2017) R. Samnakay, et al. , Appl. Phys. Lett. 106 , 023115 (2015) Figure caption: The Mo 3d spectra of MoS 2(1- x ) Te 2 x samples fabricated with different gas ambient, obtained by XPS. The bottom spectra show there is no or only subtle oxidation, whereas after the storage time, samples undergo oxidation with sample fabricated in H 2 ambient further oxidized than that fabricated in N 2 ambient. Figure 1
For < 25 nm DRAM capacitors, large cell capacitance (20 fF/cell), low leakage current density ( J ≤ 1.6×10 -7 A/cm 2 ) at the operation voltage (0.6 V), maximum process temperature < 650 o C and conformal films on a three-dimensional structure (pedestal structure) with a large aspect ratio over 30 are required. Recently, the ZrO 2 /Al 2 O 3 /ZrO 2 (ZAZ) multilayer was widely used as insulator of DRAM. [1] Al 2 O 3 has advantages of large band gap and amorphous structure, and disadvantage of low k -value. However, it is still not clear how amorphous structure and band gap of interlayer affect to leakage current property. Here, we pay attention to (Ta/Nb)O x (TN) because of its high k -value (~29), amorphous structure and low band gap (4.3 eV). [2] In this paper, we studied role of various interlayer between ZrO 2 layers on leakage current property for DRAM capacitors with TiN electrode. We fabricated four TiN capacitors with ZrO 2 /ZrO 2 (ZZ), ZAZ, ZrO 2 /(Ta/Nb)O x /ZrO 2 (ZTNZ), and ZrO 2 /(Ta/Nb)O x -Al 2 O 3 /ZrO 2 (ZTNAZ) multilayer by atomic layer deposition (ALD) and post-deposition annealing (PDA) processes. The ZrO 2 , Al 2 O 3 , and TN layers were deposited by ALD using (C 5 H 5 )Zr[N(CH 3 ) 2 ] 3 , Al(CH 3 ) 3 , and (Ta/Nb = 1/1)(NtAm)(NMe 2 ) 3 precursor, respectively, and H 2 O gas. The TNA nano-laminate layers were fabricated by alternately depositing every 1 cycle using TN and Al 2 O 3 . After multilayer fabrication, PDA was performed at 600 °C. Finally, TiN top electrode was fabricated by photo-litho. process. Fig. 1 shows relationship between CET and J at 0.6 V for all capacitors. The J values of the ZTNAZ and ZAZ capacitors decrease significantly by 10 -7 ~ 10 -8 A/cm 2 order of magnitude while ZTNZ exhibits large J of ~ 10 -5 A/cm 2 . Moreover, the J value of the ZTNAZ (CET = 1.2 nm) is lower than that of the ZAZ (CET = 1.3 nm). AFM images and RMS roughness of ZZ (CET = 1.1 nm), ZTNZ (CET = 1.2 nm), ZAZ (CET = 1.3 nm), and ZTNAZ (CET = 1.2 nm) are shown in Fig. 2. The RMS roughness of all samples exhibit almost the same value of around 1 nm. Based on these experimental data, we found that the leakage current property of capacitor is influenced by band gap width (conduction band offset of TiN) rather than amorphous structure. We conclude that the TNA is one of candidate material as interlayer for future DRAM. A part of this research is supported by CREST, JST. [1] D. Martin et al., J. Appl. Phys. 113, 194103 (2013). [2] T. Nabatame et al., J. Vac. Sci. Technol. A 33, 01A118 (2015). Figure 1
