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Biotechnology > Intro to Lithography > Flashcards

Intro to Lithography Flashcards

1
Q

Lithography

A

Transforms complex circuit diagrams into pattern w/c are defined on the wafer in a succession of exposure and processing steps to form a number of superimposed layers of insulator, conductor and semiconductors materials

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2
Q

How many lithography steps are required to fabricate a packed IC?

A

typically 8-25 steps

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3
Q

semiconductor manufacturing processes

A

design, wafer prep, front-ed processes, photolithography, etch cleaning, thin films, ion implantation, planarization, test and assembly

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4
Q

Die cut and assembly

A

good chips are attached to a lead frame package

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5
Q

soft lithography

A

uses photolithography to make a mold for PDMS (polydimethylsiloxane), w/c gets permanently bonded onto glass to make a microfluidic device; fast and cheap prototyping method

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6
Q

2 types of lithography

A

photolitography and soft lithography

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7
Q

type of lithography that makes a mold on a silicon wafer using UV light to etch a design

A

photolithography

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8
Q

type of lithography that uses the mold to make a chip from PDMS polymer

A

soft lithography

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9
Q

a unique comb. of properties resulting from the presence of an inorganic siloxane backbone and organic methyl groups attached to silicon

A

PDMS (Poly(dimethylsiloxane))

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10
Q

why are PDMS fluids iat room temp?

A

b/c they have very low galss transition

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11
Q

how can PDMS be readily converted into solid elastomers?

A

by crosslinking

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12
Q

Properties/Benefits of PDMS

A
  • Optical: transparent, optical detection from 240-1100 nm
  • Electrical: insulating, breakdown voltage (2x10^7 V/m); allows embedded surfaces, intentional breakdown to open connections
  • Mechanical: elastomeric, high youngs module (-70 kPa); conforms to surface when not polymerized, reversible deformation
  • Thermal: insulating, thermal conductivity of 0.2 W/(mk); can be used to insulate heated solutions
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13
Q

PDMS device applications

A

configurable gradient generator, valving via electrical breakdown of PDMS, cell patterning through surface modifications

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14
Q

Design saved in a DXF file format and sent to the printing company

A

SolidWorks Design

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15
Q

Fabrication of the mold (Photolitography) steps

A
  1. clean silicon wafer and dry
  2. spincoat a thin layer of SU-8 pthotoresist
  3. soft bake to evaporate the solvent
  4. align the mask
  5. flood exposure to UV light
  6. hard bake to cross-link the exposed portions of the photoresist film
  7. develop to wash away the non-exposed area of the photoresist
  8. rinse with isopropanol and dry with nitrogen gun
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16
Q

Rapid prototyping

A
  1. a system of channels is designed in a CAD program
  2. a commercial printer uses CAD file to produce a high-res transparency
  3. the transparency is used as a photomask in contact photolithography to produce a master
  4. master consists of a positive relief of photoresist on a silicon wafer and serves as a mold for PDMS
  5. liquid PDMS pre-polymer is poured over the master and cured for 1h @ 60C
  6. PDMS replica is peeled from the master
  7. replica is sealed to a flat surface to enclose the channels
17
Q

soft lithography techniques

A
  • replica molding (REM)
  • micro-contact printing
  • micro-transfer molding
  • micro-molding in capillaries
18
Q

Replica Molding

A
  1. Master mold is replicated in PDMS by casting & curing PDMS pre-polymer
  2. PDMS mold is oxidized in O2 plasma for 1 min & exposed to fluorinated silane for 2h to make a surface w/ low adhesion to PDMS
  3. PDMS is cast against this negative replica, cured and peeled off
  4. Makes positive replica of the original master
19
Q

micro-contact printing

A
  • uses PDMS stamp to form patterns of self-assembled monoplayers (SAM) on the surfaces of the substrates
  • PDMS stamp is coated with an ink of the molecules and pressed onto the solid surface
  • inking creates SAM on the solid surface
  • use of elastomers allows the micropatterned surface to come into conformal contact with the surfaces over large areas
20
Q

micro-transfer molding

A
  • PDMS stamp is filled with pre-polymer
  • excess prepolymer is removed
  • press the rubber stamp against the surface
  • cure polymer
  • peel off stamp
21
Q

micromolding in capillaries

A
  • push PDMS stamp against the substrate
  • prepolymer is applied to access holes in the mold (vacuum assisted)
  • prepolymer fills the channels using capillary forces
  • cure the polymer
  • peel off the PDMS mold
22
Q

Lithography Process

A
  1. Create PDMS Mixture
  2. Pour onto Mold and de-gas
  3. Cure the PDMS

Biotechnology (6 decks)

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