Charge Transport in Uniform Metal-Assisted Chemical Etching for 3D High-Aspect-Ratio Micro- and Nanofabrication on Silicon

Abstract

Recently, metal-assisted chemical etching (MaCE) has been proposed as a promising method for micro-and nanostructures fabrication on silicon (Si) with high aspect ratio, high geometric uniformity and low cost. In MaCE, electron holes (h + ) are injected into Si through catalytic reduction of H 2 O 2 on metal catalyst thin film patterns. Si beneath the metal is etched through a redox reaction where h + are involved. This work investigated a fundamental electrochemical process during MaCE: the transport of h + , and revealed its unique correlation with the 3D profile of the etching results. It is discovered that under the uniform etching condition, etching occurs both in the Si beneath the catalysts as well as on the sidewall of the etched space. On N-type Si, the sidewall etching is intrinsically depressed, and highly vertical HAR structures are formed; on P-type Si and undoped Si, the sidewall tapering becomes significant as the pattern number and density increase. The variation of the 3D profile can be explained by the CT during etching using a Schottky junction model, which show dependence on the intrinsic properties of the Si. CT involved in the two etching process can further be correlated by diffusion or drift of h + , which explains the influence of catalysts geometry. Fabrication of micro-and nanostructures on silicon (Si) is a key step in manufacturing of modern electronic and optoelectronic devices. Especially, the high-aspect-ratio (HAR) structures, of which the vertical dimension is much larger than the lateral dimension, enable orders-of-magnitude higher integration density and superior system performance compared to that of traditional planar structures by utilizing the space inside Si. HAR structures, such as deep trenches and deep holes, have been widely used in advanced Si-based devices. For example, deep trenches are the core structures in the microelectromechanical systems; 1 deep holes serve as the interconnect routes in the emerging 3D integration technology in microelectronic packaging. 2Most of these HAR structures are fabricated by selective removal of certain volume of Si from the bulk Si substrate, which is generally referred to as the etching of Si. Until now, the major applicable Si etching method for HAR structures fabrication is the deep reactive ion etching (DRIE). 3,4 In DRIE, Si is put in a gas chamber and etched by plasma. Although DRIE is able to fabricate a wide range of HAR structures, it is suffered from high cost. On the other hand, metal-assisted chemical etching (MaCE), a novel low-cost wet chemical etching method, has attracted attention from both academia and industry.

Tunable Surface Structuration of Silicon by Metal Assisted Chemical Etching with Pt Nanoparticles under Electrochemical Bias

“…et al in an attempt to correlate the 3D profile obtained with p-and n-type Si samples during micro-MACE with μm-sized straight-line patterns of Au as catalyst. 19 In complement to these works, our results (i) demonstrate the ohmic nature of the nanocontacts made with Pt NPs (that should also apply in the case of Au), (ii) rationalize the effect of h + injection in the case of p-type Si as a polarization of the bulk, and thus (iii) explain the various morphologies obtained by MACE (cone-shaped pores, tapered nanowires, etc. ).…”

Interfacial Contact is Required for Metal‐Assisted Plasma Etching of Silicon

“…Si covered by the noble metal catalyst etches significantly faster than uncovered Si, transferring the pattern of the deposited metal catalyst to the underlying Si. MACE proceeds through electrochemical and mass transport reactions predicated on the reduction of H 2 O 2 at the metal surface and extraction of electrons from underlying Si, thus injecting holes, at the Si–metal interface to create electron‐poor depletion regions in Si that are more susceptible to etching by HF …”

Direct Imprinting of Porous Silicon via Metal‐Assisted Chemical Etching

“…[19][20][21] Unlike its counterparts, it can "cut through" all crystal planes selectively, [ 22 ] turning it into a good candidate for the development of an imprinting process. [26][27][28][29][30][31] Moreover, while pore formation in silicon can be obtained via MACE during the etching process, the range of pore morphologies is limited and often dependent upon the doping concentration and ratio of oxidizing to reducing species. [ 25 ] A large portion of MACE research focuses on understanding defect generation, namely pores that are created in the substrate, via fundamental studies.…”