<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Fine particles of titanium ignite very easily. Aluminum and many
other metal particles do the same but little less vigorously.
Vacuum chamber surfaces coated with titanium oxidize rapidly giving
rise to "popping" sound if the vacuum system is opened in room air
immediately after deposition. That is why Ti deposition SOPs
require a delay in opening the chamber to room air after venting it
using N2. Cleaning vacuum system that is used for Ti deposition
creates hazardous situation, particularly if very powdery matter is
present. <br>
<br>
Speculation on what happened: (1) Static electricity could be a
culprit but then the ignition would occur during other non-titanium
cleaning operations at other similar fab stations. (2) Wipes
heavily soaked in isopropyl alcohol and the waste basket overwhelmed
with alcohol vapor might have denied titanium particles access to
oxygen. This is OK as long as the wipes with Ti particles sit in the
basket and slowly dry/oxidize. Turbulence created by dropping more
wipes in the basket might have brought some dry fine particles of
titanium in contact with oxygen in the turbulence resulting in
ignition. <br>
<br>
Allowing system surfaces to oxidize slowly for an extended time may
reduce chances of this happening again. Typically this is what
you would do: Vent the chamber using dry nitrogen at the end of the
day but DO NOT EXPOSE IT TO ROOM AIR. Thus, do not raise the bell
jar chamber or open the chamber door/window that opens to room air.
Allow the system to remain at atmospheric pressure overnight.
Residual oxygen in the chamber will oxidize titanium deposits
slowly. Chamber can be wiped next day using IPA/Water mixture and
vacuumed. Some extra pumping, baking, pre-coating may be required
to attain previous levels of vacuum when the system is reused for
processes. <br>
<br>
Allow an old fashioned chamber to "wait" similarly at atmospheric
pressure before cleaning if opening it to air immediately after
deposition is necessary to take out the samples/wafers.<br>
<br>
You may consider using thin aluminum foil shields if possible that
minimize need for cleaning the particle matter. Some change in
cleaning interval protocol (cleaning more often) may be needed to
avoid build up of excess loose titanium. Exposing the chamber to
residual oxygen in between deposition runs might help to reduce the
formation of atomically clean Ti particles. <br>
<br>
Hope this helps.<br>
Pramod <br>
<br>
Pramod C Karulkar Ph. D.
<br>
Home 2*5*3* 3*0*3 0*4*1*8
<br>
6024 33rd Street Ct NW
<br>
Gig Harbor WA 98335 <br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 5/6/2013 6:49 AM, Morrison, Richard
H., Jr. wrote<br>
</div>
<blockquote
cite="mid:D3862732F46DEB4B93B4A7A80614D288099B041E@mbx2.draper.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<meta name="Generator" content="Microsoft Word 12 (filtered
medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri","sans-serif";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
<div class="WordSection1">
<p class="MsoNormal">Hi Everyone,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Last week one of the staff was wiping off
some evaporator parts that were covered with Titanium metal.
He was using texwipes soaked with IPA. He tossed the texwipes
in the trash then accidentally dropped some wipes saturated
with IPA on top of them and a fire started. It self
extinguished after 1 minute but it melted the bottom of a
plastic trash can.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Have any of you had that happen or
something similar? Needless to say this is very alarming and I
need to understand what could have caused this and develop a
corrective action plan.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Rick<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Draper Laboratory<o:p></o:p></p>
<p class="MsoNormal">Group Leader Microfabrication Operations<o:p></o:p></p>
<p class="MsoNormal">555 Technology Square<o:p></o:p></p>
<p class="MsoNormal">Cambridge Ma, 02139-3563<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a class="moz-txt-link-abbreviated" href="http://www.draper.com">www.draper.com</a><o:p></o:p></p>
<p class="MsoNormal"><a class="moz-txt-link-abbreviated" href="mailto:rmorrison@draper.com">rmorrison@draper.com</a><o:p></o:p></p>
<p class="MsoNormal">W 617-258-3420<o:p></o:p></p>
<p class="MsoNormal">C 508-930-3461<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
labnetwork mailing list
<a class="moz-txt-link-abbreviated" href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a>
<a class="moz-txt-link-freetext" href="https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork">https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork</a>
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">-- </pre>
</body>
</html>