Electrochemical Microfabrication without

Photolithography – a Sustainable Manufacturing Process

S. Roy

Prof of Electrochemical Nanomaterials

School of Chemical Engineering and Advanced Materials

Institute of Nanoscale Science and Technology

University of Newcastle

Merz Court

Newcastle, NE1 7RU

Standard Photolithographic Process

A UV- sensitive resin is used

Substrate is covered with

resin

Substrate is exposed to UV-

light

The resin is either cured or

destroyed

The resin is developed

Selected areas of substrate

are left covered with resin

Sustainability Issues

• Standard lithography techniques use a host of chemicals

(which are mainly subtractive) – Waste!

• Standard lithography is multi-step slow process – for each

design new process is developed – Slow!

• Clean rooms are expensive, require planning permissions and

licensing – impacts on SMEs – Dear!

• The issue is R-R-R (Reduce – Recycle – Reuse) : Can we

improve the sustainability of microfabricated products by RRR

• Can we stop the use of photolithography of each substrate?

• EnFACE Concept : Photolith the counter electrode!!!

Maskless Pattern Transfer : Concept

Patterned Metallic Tool (Counter Electrode) and a Fully Exposed Substrate

Place in close Proximity and Plate/Etch the Substrate

However, current lines diverge, and unless selective plating or etching can be

done, the process is not feasible.

Other Practical Limitations: Electrode Gap (vs. Tolerance), Pressure drop

Gas Evolution, Micro-pattern size and density (vs. aspect ratio)

Metal Plating and Etching Through Mask

Power Supply

+

-

• Current lines are guided by the “mould” and therefore plating

occurs only at selected parts (in this case exposed parts)

Photoresist

Wafer

Gold

• Take the mould away, and plating or etching proceeds

everywhere and no patterns are transferred.

Project Development

Feasibility study

• Experimental

– Experiments to determine if selective etching and plating is attainable

– If selective plating and etching chemistry is achievable and stable

– If flow system can remove products from the electrode surface

– If plating is reproducible and stable

– Reproduced by other metals and alloys

• Modelling

– To simulate process within the system,

– Understand how pattern transfer is enabled

– Determine the important parameters for pattern transfer

Pattern Transfer on Copper Substrates

• 98.5-99% pure copper

• CuSO4 solutions which were acidified or without acid

• Etching and plating experiments

• Counter electrode was copper

• Photolithographed

• Different electrolytes were used

• Flow rates were varied

• Electrode gap was changed

Electrochemical Reactor for Feasibility Study

Electrochemical System

Resist thickness

7 mm

Resist thickness

and Pattern size

much less than

Inter-electrode

Gap

Results : Effect of Current or Potential

Acidified Solution

Cell Current Control

Non-acidified Solution

Cell Current Control

Non Acidified Solution

Cell Potential Control

Results: Effect of Pulsed Potential Etching

pV ptppp tt /[V] [ms] Cycles

10 1.0 0.02 4000

10 1.0 0.01 4000

10 10.0 0.1 4000

20 1.0 0.02 4000

20 1.0 0.02 8000

20 1.0 0.02 12000

20 1.0 0.02 20000

20 1.0 0.01 4000

20 10.0 0.1 4000

Learning from Etching Experiments

• New chemistry is needed – cannot use acidified solutions

• Lower metal ion concentration

• Solutions contain no additives - non corrosive, low toxicity

• Better pattern transfer obtained by using pulse current etching

• Flow rates was important to remove reaction products

• Cell potential is similar to those used in tanks because of the

proximity of the electrode

• Sustainable and may have good electronic properties

Electrodeposition of Copper on Nickel

Metal Plating : Typical Deposition Rates

Anode Tools

Etched Copper

How Does the Process Work : Modelling

Reactor Scale Model – Millimetre Scale Pattern Scale Model - Micron

Modelling Shapes obtained in Acidified and

Non-Acidified Solutions

Input Parameters:

Electrolyte Flow Rate

Electrolyte conductivity

Pattern Size

Inter electrode gap

Electrochemical

Kinetics

Insulator Thickness

Insulator Length

Inter-electrode gap

Cathode

Anode

Domain of Current Distribution

0

02

i

Secondary Current Distribution

Current well below anodic

limiting current

Shape Evolution In Acidified Solutions

3D optical profile

Etc

h D

epth

(m

m)

Etc

h D

epth

(m

m)

Shape Evolution in Non-Acidified Solutions

Oxide formed

Where

Current and

Potential are

Highest

Current drops at bottom

And increases at the walls

Resulting in spread of oxide

Oxide continues to spread

Resulting in a cubic shape

Potential Applications and Benefits

• EnFACE Technique can be used to transfer microscale patterns

• Reactor Technology applicable to both etching and plating

• Different metal copper, nickel and some alloys have been

structured using the technique

• Reduces the use of photolithography by 90-95%

• High cost capital equipment and chemicals unnecessary

• Low material and energy consumption

• High grade infrastructure requirement can be avoided

Publications

1. S. Roy, “A Process for Manufacturing Micro- and Nano- Devices” GB0416600.5, filed on 24th July 2004. PCT/GB2005/002795, filed 19th July 2005. Application: WO2006010888, publ. date: 2006-02-02, also published as EP1778895(A1) and EP1778895(A0). Granted in the US.

2. I. Schoenenberger and S. Roy, “An Electrochemical Method for Transferring Micro-Scale Patterns without Substrate Photolithography” Electrochim. Acta, 51, 809-819 (2005).

3. S. Roy, “Fabrication of Micro and Nano Structured Materials Using Mask-Less Processes” Invited Review Paper, J. Phys. D: Appl. Phys. 40 R413-R426 (2007).

4. S. Nouraei and S. Roy, “Analysis of Micropattern Transfer without Photolithography on Substrates”, J. Electrochem. Soc., 155(2) D97-D103 (2008).

5. S. Nouraei and S. Roy, “A Design of Experiment Approach to Electrochemical Micro- fabrication” Electrochim. Acta, 54, 2444-2449 (2009).

6. S. Roy, “EnFACE: A Mask Less Process for Circuit Fabrication” Circuit World 35(3), 8-11 (2009).

Acknowledgements

• Newcastle University Workshop

• Ivo Schönenberger

• Samane Nouraei

• Todd Green

• Qi-Bai Wu

• Tri Widayatno

• David Huntley (business advice)

• EPSRC, N-Star Equity Funding, CENAMPS

Spin Out : RoyenfaceFocused on electronics production and seeking collaboration /

partnerships.