Team:Cambridge/Protocols/Substrate Preparation for Flow Coating and Spin Coating

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===Practice===
===Practice===
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Silicon substrates are cleaved using a diamond scribe to introduce a fine nick in the surface of the single silicon crystal. Then upward pressure at the nick and downward pressure at the edges of the crystal an be used to gently and precisely fracture the silicon in two.
 
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Acetone bath and sonication is achieved by placing the substrates in a rack and placing in a beaker filled with enough acetone to cover them. This is covered with foil and placed in a sonicator for 10 minutes. Following this the O2 plasma oven can be used to burn off contaminants, we used 10 minutes in this oven to make sure our samples were clean.
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'''<FONT COLOR="700000"> Cutting Silicon to Size </FONT>'''
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# Introduce a fine nick in surface of single-crystal silicon wafer
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# Gently bend upwards to precisely fracture the silicon in two
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# Repeat until desired dimensions reached
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'''<FONT COLOR="0000FF">Notes: These silicon wafers are single crystal and have one orientation(100). Introduction of a 'directed' crack 'seeds' a defect into the surface by introducing a stress concentration. Subsequent Application of bending elicits fracture propagation along the defect direction<FONT>.
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'''<FONT COLOR="700000"> Interface Cleaning </FONT>'''
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'''Acetone Bath and Sonication'''
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# Place the substrates in a rack and submerge in beaker of acetone
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# Cover with foil to prevent outside debris and sonicate at standard settings for 10mins
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'''O<sub>2</sub> Plasma'''
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# Following solvent cleaning place samples in plasma oven for 10 minutes. (time can be adjusted depending on purity levels)
[[File:Cam_O2_Plasma_Oven.JPG |200px|thumb| left | Silicon Substrates in the O2 Plasma Oven]]
[[File:Cam_O2_Plasma_Oven.JPG |200px|thumb| left | Silicon Substrates in the O2 Plasma Oven]]
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CO2 pressure washing was not performed by us, and is as simple as pointing the pressure washer and pulling the trigger. This is performed in a fumehood and uses a strong vacuum to stabilize the sample during washing.
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'''CO<sub>2</sub> Pressure Wash'''
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# Use vaccuum suction to hold down silicon wafer
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# Direct high pressure washer and pull trigger much like washing a car
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'''''Notes: This process was carried out in a fumehood to minimise all risk as there was solvent evaporation'''''
===Safety===
===Safety===

Revision as of 10:22, 29 August 2011

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Substrate preparation

Methods used to prepare the silicon substrates for flow coating and spin coating.

Theory

The silicon pieces were cut to size and treated with various methods to remove surface debris.

Note: A clean interface is essential for providing good contact for thin films.

Various methods were employed for preparation all involving an initial cleaning step followed by a finer cleaning process

Initial preparation:

  1. Wash substrates with acetone
  2. Sonicate with standard settings

This step removes organic contaminants and loosens attached debris.

Finer preparation:

  1. Bake in O2 plasma oven for 10 mins
    or
  2. High pressure jet of liquid CO2 (CO2 is used for its sublimation property at room temperature)

The first method introduces high energy oxygen radicals which oxidises surface impurities. The second physically displaces surface debris. This step should remove remaining contaminants

Note: The resulting surface though significantly improved is not defect-free but sufficient for our purposes.

It was found the most uniform films seemed to result from high pressure washing with liquid CO2 (performed by Dr Matthew Hawkeye)

Practice

Cutting Silicon to Size

  1. Introduce a fine nick in surface of single-crystal silicon wafer
  2. Gently bend upwards to precisely fracture the silicon in two
  3. Repeat until desired dimensions reached

Notes: These silicon wafers are single crystal and have one orientation(100). Introduction of a 'directed' crack 'seeds' a defect into the surface by introducing a stress concentration. Subsequent Application of bending elicits fracture propagation along the defect direction.


Interface Cleaning

Acetone Bath and Sonication

  1. Place the substrates in a rack and submerge in beaker of acetone
  2. Cover with foil to prevent outside debris and sonicate at standard settings for 10mins

O2 Plasma

  1. Following solvent cleaning place samples in plasma oven for 10 minutes. (time can be adjusted depending on purity levels)
Silicon Substrates in the O2 Plasma Oven

CO2 Pressure Wash

  1. Use vaccuum suction to hold down silicon wafer
  2. Direct high pressure washer and pull trigger much like washing a car

Notes: This process was carried out in a fumehood to minimise all risk as there was solvent evaporation

Safety

Acetone was kept in squirt bottles in the fume hood, as was the beaker containing the substrates during sonication. Foil was used to keep debris out and acetone in the beaker. The O2 plasma oven was a self contained unit, operated and loaded by Dr Matthew Hawkeye, as was the CO2 pressure washer.


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