Lithography Flashcards

1
Q

How many fully enclosed layers are needed for freely moving parts?

A

At least 2

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2
Q

Types of lithography

A
  • electron beam
  • laser
  • proton beam
  • x-ray
  • soft
  • stereo
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3
Q

negative resist

A

deposited soluble, responds to exposure by becoming insoluble (stays where the light shines, negative material height where mask is)

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4
Q

positive resist

A

deposited insoluble, responds to exposure by becoming soluble. (leaves where the light shines - positive material height where mask is)

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5
Q

serial process

A

carried out in series one step at a time

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6
Q

parallel process

A

all steps (or parts) are undertaken at the same time

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7
Q

aspect ratio

A

height : width

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8
Q

spin casting thickness is based on:

A

viscosity of resist and spin speed

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9
Q

Photo litho basic steps

A

1) resist applied on substrate, and prebaked to remove solvents
2) masks are aligned to substrate
3) exposure
4) post exposure bake
5) development washes away soluble material
6) resist can be used as a mask to pattern the underlying layer
7) resist is stripped to reveal the patterned underlying film

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10
Q

bright field mask

A

features are opaque

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11
Q

dark field mask

A

features are transparent

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12
Q

exposure system types

A
  • contact aligner
  • proximity aligner
  • projection aligner
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13
Q

contact aligner

A
  • mask and wafer in direct contact
  • 1:1
  • contact can damage mask
  • high resolution
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14
Q

proximity aligner

A
  • mask and wafer separated by a few micron gap
  • 1:1
  • lowered resolution due to increased diffraction
  • better mask lifetime due to no contact
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15
Q

projection aligner

A

mask projected using high presicion options
5:1, - 10:1
lower mask tolerance and defect requirements

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16
Q

What two ways can photoresist be used

A

subtractive, or additive patterning

17
Q

How to create a re-entrant profile for sucessful lift off?

A
  • chemical treatment of resist with toluene prior to development to decrease solubility of top portion of resist
  • bilayer resist can be created with differing solubility
  • non-columnar light source can be used to expose the resist
18
Q

raster scan

A

left to right, top to bottom

19
Q

vector scan

A

beam traverses only the image areas

20
Q

electron beam lithography

A

uses a focused beam of electrons to expose the resist and draw the pattern

21
Q

laser lithography

A

uses a focused laser beam to expose the resist and draw the pattern
- can use either raster or vector method
- lower res than e-beam but generally less $

22
Q

maskless lithography

A

uses a DLP to project images onto wafer
- speed depends on feature size but generally faster than laser lithography

23
Q

proton beam lithography

A
  • can be used the same way as electrons but has benefits because protons have greater mass and dont scatter.
  • can get high AR
  • need particle accelerator
24
Q

x-ray lithography

A
  • x-rays used as light source
  • very high AR
    expensive, requires synchrotron
25
Q

soft lithography

A

uses a pdms stamp for pattern transfer

26
Q

sterolithography

A

rapid prototypinng process
- can be laser rastered or dynamic mask