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

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==Substrate preparation==
==Substrate preparation==
Methods used to prepare the silicon substrates for flow coating and spin coating.
Methods used to prepare the silicon substrates for flow coating and spin coating.
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'''''<FONT COLOR="0000FF">Note: A clean interface is essential for providing good contact for thin films.</FONT>'''''  
'''''<FONT COLOR="0000FF">Note: A clean interface is essential for providing good contact for thin films.</FONT>'''''  
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Various methods were employed for preparation all involving an initial cleaning step followed by a finer cleaning process
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Various methods were employed during our thin film making.
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# Acetone bath and sonication followed by either by O<sub>2</sub> plasma oven or high pressure jet wash with liquid CO<sub>2</sub> (CO<sub>2</sub> is used for its sublimation property at room temperature)
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# 'Piranha Solution', a potent bath of concentrated sulphuric acid and hydrogen peroxide
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'''<FONT COLOR="700000">Initial preparation:</FONT>'''
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The methods are all either based upon cleaning up organic contaminants and debris via some chemical reaction like the introduction of oxygen radicals or by physical removal like the pressure wash.
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#Wash substrates with acetone
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#Sonicate with standard settings
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'''''This step removes organic contaminants and loosens attached debris.
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===Practice===
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'''<FONT COLOR="505050">Finer preparation:</FONT>'''
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# Bake in O<sub>2</sub> plasma oven for 10 mins
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#;or
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# High pressure jet of liquid CO<sub>2</sub> (CO<sub>2</sub> is used for its sublimation property at room temperature)
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'''''The first method introduces high energy oxygen radicals which oxidises surface impurities. The second physically displaces surface debris. This step should remove remaining contaminants'''''
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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">Note: The resulting surface though significantly improved is not defect-free but sufficient for our purposes.</FONT>'''
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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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It was found the most uniform films seemed to result from high pressure washing with liquid CO<sub>2</sub> (performed by Dr Matthew Hawkeye)
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====<FONT COLOR="700000"> Interface Cleaning </FONT>====
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[[File:Cam_O2_Plasma_Oven.JPG |200px|thumb| left | Silicon Substrates in the O2 Plasma Oven]]
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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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===Practice===
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=====O<sub>2</sub> Plasma=====
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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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# Following solvent cleaning place samples in plasma oven for 10 minutes. (time can be adjusted depending on purity levels)
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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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=====Piranha Solution=====
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[[File:Cam_O2_Plasma_Oven.JPG |200px|thumb| left | Silicon Substrates in the O2 Plasma Oven]]
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# Fill beaker with 50% HPLC grade sulphuric acid and 50% hydrogen peroxide HPLC grade
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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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# Place beaker on hot plate at 100<sup>o</sup>c
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# Place all the prepared silicon wafers within the beaker (It does not matter if the silicon wafers overlap)
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# Leave for approximately 10 mins or when bubbling subsides.  
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# When ready to spin take out desired silicon wafer for spinning, rinse with distilled water and blow dry with N<sub>2</sub> gas.  
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As explained to me by the lab researchers in the Thin Films Group absolutely nothing survives the piranha bath!
===Safety===
===Safety===
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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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* Kept acetone in squirt bottles and piranha solution in the fume hood.
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* Kept beaker containing substrates during sonication also in fume hood with foil to keep out debris
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* The O2 plasma oven and CO<sub>2</sub> pressure washer were self contained units, operated and loaded by Dr Matthew Hawkeye.
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* Always wear nitrile gloves and lab coat when handling such concentrated solutions of sulphuric acid and hydrogen peroxide.
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'''Note of advice: Carry out all work in fume hoods even if it is safe not to do so. You are working with a lot of solvents and vapours which are potentially hazardous to health. Better safe than sorry!'''
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{{Template:Team:Cambridge/CAM_2011_PROTOCOL_FOOT}}

Latest revision as of 20:36, 21 September 2011

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OVERVIEW
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Contents

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 during our thin film making.

  1. Acetone bath and sonication followed by either by O2 plasma oven or high pressure jet wash with liquid CO2 (CO2 is used for its sublimation property at room temperature)
  2. 'Piranha Solution', a potent bath of concentrated sulphuric acid and hydrogen peroxide

The methods are all either based upon cleaning up organic contaminants and debris via some chemical reaction like the introduction of oxygen radicals or by physical removal like the pressure wash.

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

Silicon Substrates in the O2 Plasma Oven
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)
Piranha Solution
  1. Fill beaker with 50% HPLC grade sulphuric acid and 50% hydrogen peroxide HPLC grade
  2. Place beaker on hot plate at 100oc
  3. Place all the prepared silicon wafers within the beaker (It does not matter if the silicon wafers overlap)
  4. Leave for approximately 10 mins or when bubbling subsides.
  5. When ready to spin take out desired silicon wafer for spinning, rinse with distilled water and blow dry with N2 gas.

As explained to me by the lab researchers in the Thin Films Group absolutely nothing survives the piranha bath!

Safety

  • Kept acetone in squirt bottles and piranha solution in the fume hood.
  • Kept beaker containing substrates during sonication also in fume hood with foil to keep out debris
  • The O2 plasma oven and CO2 pressure washer were self contained units, operated and loaded by Dr Matthew Hawkeye.
  • Always wear nitrile gloves and lab coat when handling such concentrated solutions of sulphuric acid and hydrogen peroxide.

Note of advice: Carry out all work in fume hoods even if it is safe not to do so. You are working with a lot of solvents and vapours which are potentially hazardous to health. Better safe than sorry!

Back to Protocols

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