Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers

Summary

A protocol for metal-assisted chemical imprinting of 3D microscale features with sub-20 nm shape accuracy into solid and porous silicon wafers is presented.

Abstract

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is capable of direct patterning 3D micro- and nanoscale features in monocrystalline group IV (e.g., Si) and III-V (e.g., GaAs) semiconductors without the need of sacrificial templates and lithographical steps. During this process, a reusable stamp coated with a noble metal catalyst is brought in contact with a Si wafer in the presence of a hydrofluoric acid (HF) and hydrogen peroxide (H₂O₂) mixture, which leads to the selective etching of Si at the metal-semiconductor contact interface. In this protocol, we discuss the stamp and substrate preparation methods applied in two Mac-Imprint configurations: (1) Porous Si Mac-Imprint with a solid catalyst; and (2) Solid Si Mac-Imprint with a porous catalyst. This process is high throughput and is capable of centimeter-scale parallel patterning with sub-20 nm resolution. It also provides low defect density and large area patterning in a single operation and bypasses the need for dry etching such as deep reactive ion etching (DRIE).

Introduction

Three-dimensional micro- and nanoscale patterning and texturization of semiconductors enables numerous applications in various areas, such as optoelectronics^1,2, photonics³, antireflective surfaces⁴, super hydrophobic, and self-cleaning surfaces^5,6 among others. Prototyping and mass-producing 3D and hierarchical patterns has been successfully accomplished for polymeric films by soft lithography and nanoimprinting lithography with sub-20 nm resolution. However, transferring such 3D polymeric patterns into ....

Protocol

CAUTION: Use appropriate safety practices and personal protective equipment (e.g., lab coat, gloves, safety glasses, closed-toe shoes). This procedure utilizes HF acid (48% wt) which is an extremely hazardous chemical and requires additional personal protective equipment (i.e., a face shield, natural rubber apron, and second pair of nitrile gloves that covers the hand, wrists, and forearms).

1. Stamp preparation for Mac-imprint

1. PDMS mold fabrication
   1. Prepare the RCA-1 solution by mixing deionized pure (DI) water and ammonium hydroxide in the glass beaker in a 5:1 ratio (volume). Place the beaker with ....

Results

Scanning electron microscope (SEM) images, optical microscope scans (Figure 9), and atomic force microscopy (AFM) scans (Figure 10) were obtained in order to study the morphological properties of the Mac-Imprint stamps and imprinted Si surfaces. The cross-sectional profile of the imprinted solid Si was compared to that of the used porous Au stamp (Figure 10). Pattern transfer fidelity and porous Si g.......

Discussion

Mac-Imprint stamps and prepatterned Si chips (p-type, [100] orientation, 1-10 Ohm∙cm) were prepared according to sections 1 and 2 of the protocol, respectively. The Mac-Imprint of prepatterned Si chip with stamps containing 3D hierarchical patterns was performed according to section 3 of the protocol (Figure 9). As shown in Figure 9a, different configurations of Mac-Imprint were applied: solid Si with solid Au (left), porous Si with solid .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetone, >99.5%, ACS reagent	Sigma-Aldrich	67-64-1	CAUTION, chemical
Ammonium fluoride, >98%, ACS grade	Sigma-Aldrich	12125-01-8	CAUTION, hazardous
Ammonium hydroxide solution, 28-30%, ACS reagent	Sigma-Aldrich	1336-21-6	CAUTION, hazardous
AZ 400K developer	Microchemicals	AZ 400K	CAUTION, chemical
BenchMark 800 Etch	Axic	BenchMark 800	Reactive ion etching
Chromium target, 2" x 0.125", 99.95% purity	ACI alloys	ADM0913	Magnetron sputter chromium target
CTF 12	Carbolite Gero	C12075-700-208SN	Tube furnace
Desiccator	Fisher scientific Chemglass life sciences	CG122611	Desiccator
F6T5/BLB	Eiko	F6T5/BLB 6W	UV bulb
Gold target, 2" x 0.125", 99.99% purity	ACI alloys	N/A	Magnetron sputter gold target
Hotplate KW-4AH	Chemat Technology	KW-4AH	Leveled hotplate with uniform temperature profile
Hydrofluoric acid, 48%, ACS reagent	Sigma-Aldrich	7664-39-3	CAUTION, extremly hazardous
Hydrogen peroxide, 30%, ACS reagent	Fisher Chemical	7722-84-1	CAUTION, hazardous
Isopropyl alcohol, >99.5%, ACS reagent	LabChem	67-63-0	CAUTION, chemical
MLP-50	Transducer Techniques	MLP-50	Load cell
Nitric acid, 70%, ACS grade	SAFC	7697-37-2	CAUTION, hazardous
NSC-3000	Nano-master	NSC-3000	Magnetron sputter
Potassium hydroxide, 45%, Certified	Fisher Chemical	1310-58-3	CAUTION, chemical
Rocker 800 vacuum pump, 110V/60Hz	Rocker	1240043	Oil-free vacuum pump
Silicon master mold	NILT	SMLA_V1	Silicon chip with pattern
Silicon wafers, prime grade	University wafer	783	Si wafer
Silver target, 2" x 0.125", 99.99% purity	ACI alloys	HER2318	Magnetron sputter silver target
SP-300	BioLogic	SP-300	Potentiostat
SPIN 150i	Spincoating	SPIN 150i	Spin coater
SPR 200-7.0 positive photoresist	Microchem	SPR 220-7.0	CAUTION, chemical
Stirring hotplate	Thermo scientific Cimarec+	SP88857100	General purpose hotplate
SU-8 2015 negative photoresist	Microchem	SU-8 2015	CAUTION, chemical
SYLGARD 184 Silicone elastomer kit	DOW	4019862	CAUTION, chemical
T-LSR150B	Zaber Technologies	T-LSR150B-KT04U	Motorized linear stage
Trichloro(1H,1H,2H,2H-perfluorooctyl)silane (PFOCS), 97%	Sigma-Aldrich	78560-45-9	CAUTION, hazardous