Formation of Through-Holes in Si Wafers by Using Anodically Polarized Needle Electrodes in HF Solution

Abstract

Electrochemical pore formation in Si using an anodized needle electrode was studied. In the electrochemical process, a Pt, Ir or Pd needle with a diameter of 50-200 μm was brought into contact at its tip with a Si wafer, which was not connected to an external circuit, in HF solution. By applying an anodic potential to the needle electrode against a Pt counter electrode, a pore with a diameter slightly larger than the diameter of the needle electrode was formed in both p-type and n-type Si, of which current efficiency was higher for n-type Si. Through-holes were electrochemically formed in p-type and n-type Si wafers at speeds higher than 30 μm min(-1) using a sharpened Ir needle electrode. A model was proposed to explain the results, in which the pore formation was attributed to successive dissolution of Si atoms near the 3-phase (Si/metal/HF solution) boundary by positive holes injected from the needle electrode to the surface of Si.

Porous Silicon Formation by Metal Nanoparticle-Assisted Etching

“…Silicon nanostructures obtained by MAE has been successfully used in lithium rechargeable batteries (Ripenbein et al 2010;McSweeney et al 2011;Liu et al 2011), nanocapacitors (Chang et al 2010), diffusion membrane applications (Cruz et al 2005;Chen et al 2011), formation of nanostructured adhesive metal film on porous Si surface (Yae et al 2010b(Yae et al , 2011a, production of Si powders (Loni et al 2011), porous Si nanowires with photocatalytic properties (Qu et al 2009(Qu et al , 2010, and biosensing chips (Xiao et al 2013). The catalytic properties of Pt have been used to develop a slicing method showing the possibility to produce Si wafers from an ingot (Salem et al 2010) or to form through a hole in Si (Sugita et al 2011). MAE combined with patterning of metal catalyst thin film deposition is widely used to form regularly organized nanostructures on Si (Yae et al 2010a;Asoh et al 2007aAsoh et al , b, c, 2008Asoh et al , 2009Bauer et al 2010;Peng et al 2007;Ono et al 2007Ono et al , 2009Pacholski 2011;Scheeler et al 2012;Chattopadhyay and Bohn 2004;Hung et al 2010;Lee et al 2011) or arrays of vertically standing Si nanowires with controlled diameter and controlled distances between them (Huang et al 2007(Huang et al , 2010bPeng et al 2007;Lévy-Clément et al 2011;McSweeney et al 2011;Qu et al 2009Qu et al , 2010Zhang et al 2008;Chang et al 2009;…”

3D patterning of silicon by contact etching with anodically biased nanoporous gold electrodes

“…Hence, the Si sample is no longer part of the EC cell. Grooves and through-holes could be etched in wafers using these "catalytic" metal wires [3][4][5][6][7]. With a 200 µm Pt wire polarized at 2.25 V vs. Ag/AgCl, the dissolution rate was 2.4 µm min -1 for an etched area of 0.03 mm 2 [6].…”

3D Patterning of Si by Contact Etching With Nanoporous Metals

“…The major problem encountered with electrochemical contact etching at the macroscopic scale is the diffusion of the electrolyte. Because the metal and silicon phases must be in intimate contact, there is no room for the diffusion of the electrolyte and consequently, as reported by Sugita et al (2011), etching must proceed laterally from the solution bulk to the center of the metal tool, which slows down the in-depth etch rate. This problem is not severe when imprinting a single element with a diffusion path length of a few tenths of μm, (~wire diameter), but rather insurmountable for a “flat” contacting surface area of say a few cm 2 .…”

“…They used a platinum wire, 50 μm in diameter, anodically polarized against a counter-electrode in a HF solution and brought in contact with silicon to make cuts a few millimeters deep. Since then, grooves and through-holes have been etched using metal wires or tips as etching tools (Lee et al, 2009, 2011; Salem et al, 2010; Sugita et al, 2011, 2013). Another example of contact etching with a platinum needle has been given by Imamura et al (2015).…”