Ohmic Contact Formation of Sputtered TaN on n-Type Ge with Lower Specific Contact Resistivity

Abstract

Modulation of the effective Schottky barrier height of Al/TaN/n-Ge Schottky junctions by varying TaN thickness and ohmic contact formation on n-type Ge substrates is reported. A specific contact resistivity of 2.7×10 −5 · cm 2 is achieved for a Al/TaN(400/15 nm) layer on moderately doped n-type Ge, which is smaller by two orders of magnitude compared with that of an Al layer (1.2×10 −3 · cm 2 ) in direct contact with the same wafer. Sputtering a thin TaN layer on n-Ge effectively improves the contact resistivity of a metal/n-Ge contact by significantly reducing the effective Schottky barrier height, facilitating the fabrication of high-performance Ge devices. Germanium (Ge) is considered as one of the most promising materials due to its high electron and hole mobilities in electronic and photonic device applications. The metal-oxide-semiconductor fieldeffect transistor (MOSFET) with Ge channel facilitates the fabrication of next generation high-mobility devices. 1,2 Despite significant progress in the p-channel Ge MOSFET, the n-channel Ge MOSFET still suffers from serious challenges. 3,4 Non-ohmic or high-resistivity contacts for metal/n-Ge are roadblocks for Ge-based complementary metal-oxide semiconductor technology. 5 Low-resistivity contacts of metal/n-Ge are difficult to achieve due to the high Schottky barrier height (SBH) caused by the strong Fermi-level pinning (FLP) and low activation limits as well as the concentration-enhanced diffusion of n-type dopants in Ge. 6 Strong FLP at the charge neutrality level close to the valence band edge of Ge results in a high electron SBH on n-type Ge, independent on the work function of the metal and presents a high contact resistance. [6][7][8] Several methods have been proposed to alleviate the FLP effect and obtain the ohmic contact for n-Ge such as using sulfur-passivated metal germanide 9 or germanium nitridation 10 or inserting an ultrathin insulator interlayer (e.g., Al 2 O 3 , 11 SiN, 12 GeO x or AlO x , 13 and TiO 2 , 14 among others). Although an ultra-thin insulator interlayer can decrease the effective SBH for metal/insulator/n-Ge, the thickness of the insulator must be strictly maintained in the range of 0 ∼ 8 nm for TiO 2 , 14 and in the range of 0 ∼ 1 nm for the other insulators such as Al 2 O 3 , etc. 11 However, a specific contact resistivity (ρ c ) of 1×10 −2 · cm 2 is too high 15 for n+ source/drain contacts in Ge nMOSFET. Recently, an ohmic contact formation was obtained by directly depositing TiN on an n-Ge wafer, but no ρ c was reported. 16 In the present paper, we prepared Al/TaN/n-Ge Schottky junctions to investigate SBH modulation by varying the TaN thickness. Given that the metallic property of TaN does not introduce a significant tunneling resistance, TaN thickness can be varied in a wide range without increasing the tunneling resistance. Thus, a low ρ c of TaN directly sputtered on n-type Ge is achieved. ExperimentalTo study SBH modulations by varying TaN thickness, Schottky diodes were fabricated using n-type Ge(100) substrates with resisti...

High Performance Germanium n⁺/p Shallow Junction for the Scaled nMOSFET

“…3). Compared to our previous results for the samples annealed by rapid thermal annealing [3], the value of ρ C is improved by about three orders of magnitude. Ge n + /p diodes (I on /I off ~ 2x10 5 with an ideality factor η ~1.28) realized using ELA (Fig.…”

Research progress in the epitaxial growth of silicon-based group IV materials, and their light emitters and photodetectors

“…由于Ge材料具有很高的 表面态密度, 单质金属与Ge接触会存在强烈的费米钉 扎效应 [44] , 从而导致金属/n-Ge的接触势垒很高, 难以 获得好的欧姆接触. 本课题组研究了化合物金属TaN 材料与n-Ge的接触, 通过金属/n-Ge之间插入超薄TaN 薄膜, 将接触势垒高度由~0.6 eV降低到0.44 eV, 比接 触电阻率降低了两个数量级 [45,46] . 化合物金属TaN与单 质金属不同, 其与n-Ge的接触界面会形成偶极子层且 从0.12 A/W提高到0.3 A/W [47] .…”

A study on NiGe-contacted Ge n+/p Ge shallow junction prepared by dopant segregation technique

“…Furthermore, the effective oxide thickness (EOT) has been reduced to thinner than 1 nm by depositing different high-k materials [12,13]. However, the progresses about the n + /p shallow junction and the low contact resistance of the metal/nGe contact are not as successful as that about the gate dielectric [7,14,15]. Strong Fermi-level pinning effect fixes the Fermi-level close to the valence band edge of Ge so that the Schottky barrier height of the metal/n-Ge contact is around 0.6 eV [5].…”

“…For example, by inserting a thin interfacial layer between metal and Ge such as Si, TiO 2 , ZnO, Y 2 O 3 , TaN, and WSi, the Schottky barrier height can be reduced but in some cases, the contact resistance remains large due to the added series resistance from the interfacial layer [14,[19][20][21][22][23]. The lowest contact resistivity obtained by the interfacial layer insertion method is 1.4 Â 10 À7 X cm 2 , which is achieved by ZnO-insertion and also doping the interfacial layer [21].…”