Labs Flashcards
How do we classify the vacuum?
Pressure Low 10^3 -1 mbar Medium 1-10^-3 mbar High 10^-3-10^-7 mbar Ultra high 10^-7-10^-14
What are the definitions of number density, mean free path and particle flux?
Number density - quantity of gas per unit volume
Mean free path - average distance between collisions
Particle flux - rate at which particles hit the surface
How do we specify flow numerically?
Viscous
Transitional
Molecular
How many types of pumps are generally included in a vacuum system?
2 - primary, secondary
What are the methods used to measure vacuum?
Gauges
What are the vacuum gauges used to measure low, high and ultra-high vacuum?
low - diaphragm
high - schultz-phelps
ultra-high - hot cathode
How many types of thin film deposition methods are using mostly in nowadays?
physical
chemical
mixed
What are the principles of sputtering and e-beam evaporation processes?
Sputtering - mixed, noble-gas mixed with plasma forming gas
Ebeam - physical deposition
What are the differences between DC magnetron sputtering and RF sputtering?
DC vs AC
What are the main components of sputtering and e-beam evaporation systems (including pumps, gauges etc)?
Power source, primary, secondary pump, magnetron, sample stage, electron gun
What is lithography?
Pattern transfer
What types of lithography are used depending on radiation sources?
Photo
xray
ion beam
ebeam
What are the main stages of a photolithograph process?
Photoresist coating, alignment and exposure, development
Why do we need resist materials?
Restricts the etchant and prevents it from attacking the substrate
What are the main requirements for the resist material?
High resolution, high etch resistance, good adhesion, wider process latitude
What are the differences between negative and positive photoresist?
Negative - becomes insoluble after exposure, unexposed parts dissolve during developing
Positive - becomes soluble after exposure, exposed parts dissolve during developing
What will effectively limit the feature size?
Alignment
What is the minimum feature size which can be achieved using mercury lamp?
0.25 um
Which are the main performance metrics of a patterning process?
Resolution - minimum feature size
Registration - how regularly patters are aligned
Throughput - number of wafers that can be exposed
Which alignment tools are commonly used?
Contact printer
Proximity printer
Projection printer
Stepper
What is the definition of etching process?
Permanent transfer of pattern from mask onto substrate
What are etching methods used in thin film patterning processes?
Wet etching
Dry etching
Lift-off
What are the important etching parameters?
Etch rate, uniformity, throughput, selectivity
What are figures of merit of etching process?
Uniformity,
selectivity
anisotropy
What is the principle of RIE process?
Reactive ion etching - no field in centre
What are the advantages and disadvantages of lift-off and ion etching processes?
Lift-off - cheap, short, easy, low anisotropy, low adhesion, low repeatability, high selectivity
Ion etching - expensive, long, high degree of anisotropy, good adhesion, high repeatability, low selectivity
What type of photoresist is used for lift-off and ion etching processes?
?
What are major steps occur in a RIE process?
?
Which main factors will affect the etching rate in the RIE process?
Sample distance, angle
Voltage
What are the main components of a RIE system (including pumps, gauges etc)?
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