Lithography

Question 1

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

Answer 1

At least 2

Question 2

Types of lithography

Answer 2

• electron beam
• laser
• proton beam
• x-ray
• soft
• stereo

Question 3

negative resist

Answer 3

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

Question 4

positive resist

Answer 4

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

Question 5

serial process

Answer 5

carried out in series one step at a time

Question 6

parallel process

Answer 6

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

Question 7

aspect ratio

Answer 7

height : width

Question 8

spin casting thickness is based on:

Answer 8

viscosity of resist and spin speed

Question 9

Photo litho basic steps

Answer 9

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

Question 10

bright field mask

Answer 10

features are opaque

Question 11

dark field mask

Answer 11

features are transparent

Question 12

exposure system types

Answer 12

• contact aligner
• proximity aligner
• projection aligner

Question 13

contact aligner

Answer 13

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

Question 14

proximity aligner

Answer 14

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

Question 15

projection aligner

Answer 15

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

Question 16

What two ways can photoresist be used

Answer 16

subtractive, or additive patterning

Question 17

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

Answer 17

• 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

Question 18

raster scan

Answer 18

left to right, top to bottom

Question 19

vector scan

Answer 19

beam traverses only the image areas

Question 20

electron beam lithography

Answer 20

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

Question 21

laser lithography

Answer 21

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 $

Question 22

maskless lithography

Answer 22

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

Question 23

proton beam lithography

Answer 23

• 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

Question 24

x-ray lithography

Answer 24

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

Question 25

soft lithography

Answer 25

uses a pdms stamp for pattern transfer

Question 26

sterolithography

Answer 26

rapid prototypinng process
- can be laser rastered or dynamic mask