Producing Microscale Ge Textures via Titanium Nitride‐ and Nickel‐Assisted Chemical Etching with CMOS‐Compatibility

Abstract

on Ge has been explored as a promising alternative to traditional etching techniques. For example, Kim et al. [9] employed a thin Au layer as catalyst to realize pyramidal and indentation antireflection textures on Ge which contributed to enhance responsivity of near infrared (NIR) photodetectors. Lee et al. [10] coated a thin Ag layer on Ge and realized the formation of random antireflection structures by MacEtching in H 2 O 2 /HF/AgNO 3 solution. Shin et al. [11] also fabricated Ge nano-cone array using a thin Ag catalyst layer, followed by MacEtching in HF/H 2 O 2 .It should be emphasized that metal catalyst layer such as widely-used Au and Ag plays a crucial role for the MacEtch process of Ge, since it catalyzes the reduction of oxidant in the solution (normally H 2 O 2 and KMnO 4 ) to generate holes for subsequent etching. Although MacEtch of Ge based on those noble metal catalysts has been well explored, the usage of those noble metals is still a major drawback for the integration of Ge MacEtch in the current industrial front and back end of the line in the complementary metal oxide semiconductor (CMOS) fabrication process because deep-level defects are generated by non-CMOS compatible metals. [12][13][14] Many researchers have delved into the uncharted territory in order to identify the suitable CMOS-compatible catalyst for Ge MacEtch. For example, Li et al. [15] investigated the formation of Ge nanostructures by wet etching assisted by graphene. Nakade et al. [16,17] employed reduced graphene oxide to boost Ge wet etching in water. However, graphene-and graphene oxide-assisted chemical etching of Ge suffer from low etch rate (20-30 nm h −1 even when heated up) and poor morphologies, which make it unsuitable for mass production of uniform nanostructures. Therefore, it is worthwhile to explore novel etching catalysts with high efficiency and CMOS-compatibility.Titanium nitride (TiN) is widely used in CMOS process as local interconnects and barrier layers because it is chemically stable, [18] highly conductive, and has a work function of 4.5 eV. [19] These properties make it also suitable as the catalyst which can boost various chemical reactions. [20,21] As the pioneering work employing TiN as catalyst in wet etching, Kim et al. [22] have proven its effectiveness in the fabrication of highly ordered Si nanopillars. However, etching characteristic of TiN-MacEtch is different when compared with typical Au-MacEtch. Mass transport underneath the TiN is significantly limited due to its strong adhesion, leading to etching in area not covered by TiN, similar As an emerging anisotropic wet etching technique, metal-assisted chemical etching (MacEtch) has been widely employed for fabricating nano-and micro-structures of germanium (Ge) for potential infrared (IR) photonics and optoelectronics. However, traditional noble metal catalysts such as Au and Ag limit its application in complementary metal oxide semiconductor (CMOS) processes, as Au is considered as a detrimental deep-level impurity in Ge. In this work, the fe...

A heavily doped germanium pyramid array for tunable optical antireflection in the broadband mid-infrared range

“…35 TiN meshes served as a catalyst in the MacEtch process. 17 The schematic process mechanism of the MacEtch is shown in Fig. S5(a and b) (ESI †).…”

“…16 In addition, the pyramid surfaces show low reflectance, which is similar to the nanowire surfaces. 17 However, such antireflective structures suffer from low reflectance in the MIR range, which is critical for chemical detection, target recognition, and fundamental studies of cavity quantum electrodynamics. 18 Alternatively, the metasurface is an attractive candidate, which can tune the reflectance and transmittance windows by changing the geometric conditions.…”

“…16 In addition, the pyramid surfaces show low reflectance, which is similar to the nanowire surfaces. 17 However, such antireflective structures suffer from low reflectance in the MIR range, which is critical for chemical detection, target recognition, and fundamental studies of cavity quantum electrodynamics. 18…”

Inverse metal-assisted chemical etching of germanium with gold and hydrogen peroxide

“…Recent publications on applications of MACE to Ge photodetectors focus on creating closely spaced roughening features on the scale of a micron, close to the the wavelength of light for telecommunications [22,23]. Creation of periodic arrays of nanopyramids to reduce reflectivity has been demonstrated in the mid-infrared and beyond [29][30][31]. Lu et al used HF and H 2 O 2 as the etchant and silver (Ag) as the metal catalyst [22].…”

Direct Chemisorption-Assisted Nanotransfer Printing with Wafer-Scale Uniformity and Controllability

“…The nanostructures are transferred onto various semiconductor substrates (Si, glass, GaAs, and Ge) for demonstrating the wide applicability of our method. In addition, we fabricate controllable nanostructures with extremely high aspect ratios (HARs) by applying CF-nTP to metal-assisted chemical etching (MacEtch). − This combination can create a precedent for well-defined nanostructures with HAR. More notably, the proposed combination will replace conventional techniques involving the fabrication of metal catalysts ( e.g.…”