New material request: polystyrene microspheres in aqueous suspension

Ed Myers edmyers at
Mon Oct 22 10:04:46 PDT 2007


Yes, it is true latex microspheres are not new to 
the fab.  There is however limitations on how and 
where they can be used in the fab.  Please do not 
take this approval as an open approval for 
microspheres, just approval of your outlined 
process flow.   It is important the spheres be 
brought in to the fab in solution and not in the dry form.

Reviewing your proposed process, the sphere 
ashing should be done in Dryteck 1.  You must 
also collect your Ag etchant locally.  This 
includes all of the rinse water as well.  None of 
the Ag solutions are allowed to be aspirated or 
dumped down the drains.  Remember any solutions 
which are brought in to the fab needs to have a 
yellow chemical label.  These can be picked up from Manhaz.

I am aware I've been very derelict in my specmat 
responsibilities.  I apologize for this.


At 09:12 AM 10/22/2007, Aaron Hryciw wrote:
>Hello –
>I've been talking with James Conway during Raith 
>training, and he has told me that 
>unfucntionalised latex microspheres are actually 
>not a new material for SNF, since they are 
>already used in the e-beam lab, etc.  As such, I 
>assume that there is no problem with my using 
>the spheres in the lab, so long as the rest of 
>my process is compatible with SNF procedures.
>  – Aaron
>On 10/10/07, Aaron Hryciw <<mailto:ahryciw at>ahryciw at> wrote:
>Dear SpecMat Committee –
>Please regard this email as a request for a new 
>material for use at SNF; a general MSDS for this 
>class of materials (from the chemical supplier 
>from whom the material has been purchased) is attached.
>Contact information
>Aaron Hryciw
>Coral login:  ahryciw
>Phone:  3-5840 (office); (650) 353-0347 (cell)
><mailto:ahryciw at>ahryciw at
>PI:  Mark Brongersma (Mat. Sci. Eng.)
>Chemical or material name
>Polystyrene microspheres (diameters between 100 
>nm and 1 um) suspended in DI water, 10% solids by weight, 15 mL vials.
>MSDS from supplier attached.
>Will be diluted with methanol or ethanol before use.
>Common/trade names:  polymer microsphere 
>suspension, polystyrene microspheres, 
>polystyrene nanospheres, latex microspheres suspensions.
>Storage group identifier:  G. Non-Reactive 
>Materials and Non-Hazardous Materials.
>Main hazard class:  11. Non Hazardous.
>Vendor/manufacturer info
>Duke Scientific Corporation
>2463 Faber Place
>P.O. Box 50005
>Palo Alto, CA
>Phone: 1-800-334-3883 or 1-650-424-1177
>Fax:  1-650-424-1158
><mailto:info at>info at
> (in 
>Reason for request
>My interest in polystyrene microspheres is due 
>to their use as a self-assembled monolayer mask, 
>as a means of fabricating large (~cm^2) arrays 
>of silicon nanowires (NWs) with controlled size, 
>length, and areal density (please refer to Huang 
>et. al, attached).  Nanosphere lithography (NSL) 
>comprises a rapid, parallel approach to 
>fabricating well-controlled NWs without 
>requiring conventional photolithographic 
>techniques.  The material used for the mask 
>(viz., the polystyrene microspheres) is also 
>very benign and poses no health or safety 
>hazards when used properly for this technique.
>Process Flow
>I intend to follow the general process flow 
>detailed in the attached paper ( Huang et. 
>al).  if necessary, the entire process flow 
>needn't occur in SNF (only use of the RIE tool 
>is strictly required), although, for the sake of 
>cleanliness, I would prefer it.
>A full process flow in SNF would be as follows:
>Clean (100) n-type Si wafers or pieces (ca. 1x1 
>cm^2) in an ultrasonic cleaner using acetone (10 min), then methanol (5 min).
>Clean in Piranha (4:1 v/v H2SO4:H2O2) and RCA 
>solution (1:1:5 v/v/v NH3:H2O2:H2O @ 80 °C) for 1 hr.
>Rinse in DI water.
>Place substrate in a Petri dish (I will have my 
>own dedicated glassware) and cover with DI water.
>Pipette polystyrene microsphere solution (5% 
>solids in 15 mL DI water + 15 mL methanol) onto 
>water surface and gently tilt Petri dish to 
>encourage self-assembly of large single-crystal hcp arrays.
>Allow water to evaporate slowly, depositing 
>microspheres onto substrate. [The foregoing six 
>steps could be performed at wbgeneral, wbmetal, or wbnonmetal, as necessary.]
>RIE microsphere array to desired sphere diameter 
>using O2 plasma etch:  40 sccm, 30 W RF power, 5 
>Pa pressure. [Performed on one of the drytek 
>tools, consistent with previous material groups.]
>Deposit 40 nm of Ag. [innotec or metallica]
>Etch Si NWs in an etchant consisting of HF (4.6 
>M) , H2O2 (0.44 M), and H2O. [wbgeneral]
>Remove microspheres by soaking in toluene for 2 hr. [wbsolvent]
>Remove Ag film by soaking in nitric acid for 15 min. [wbgeneral]
>If necessary, steps 1–6 and 7–11 could be 
>performed outside SNF (in our lab in McCullough Bldg., for instance).
>Amount and form
>Two or three 30-mL vials containing microspheres 
>(of two or three different sizes) suspended in 
>15 mL DI water + 15 mL methanol.  Once the 15-mL 
>DI-water-suspended material (as purchased) has 
>been diluted with methanol, no further mixing will be required.
>If the entire process flow is approved for use 
>in SNF, I would store the vials of microsphere 
>aqueous/methanoic suspensions at SNF.  If only 
>step 7 is approved for SNF, I would store them in our group's lab.
>As per the MSDS, waste materials containing 
>microspheres could be disposed of in SNF's 
>hazardous materials bins in a sealed, labeled 
>plastic bag, due to their non-hazardous nature.
>Thank-you for considering this new material for 
>use at SNF.  I would enjoy the opportunity to 
>discuss possible amendments to the 
>abovementioned process flow if necessary to allow it in the cleanroom.
>Best regards,
>  – Aaron
>Aaron Hryciw
>Postdoctoral Scholar
>Geballe Laboratory for Advanced Materials
>Stanford University
>476 Lomita Mall (04-490)
>McCullough Building, Rm. 325
>Stanford, CA  94305-4045
>Tel.:  (650) 723-5840
>Fax.:  (650) 736-1984
>Aaron Hryciw
>Postdoctoral Scholar
>Geballe Laboratory for Advanced Materials
>Stanford University
>476 Lomita Mall (04-490)
>McCullough Building, Rm. 325
>Stanford, CA  94305-4045
>Tel.:  (650) 723-5840
>Fax.:  (650) 736-1984

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