Mid-Term November 13, 2012
MAE 252—Marc Madou
1. Microfabrication History:
a. MEMS and NEMS constitute a large fraction of the semiconductor
device market? True or false? FALSE
b. A bipolar transistor is a higher impedance device than a CMOS
transistor? True or false? FALSE
c. The operation of the transistor is the transfer of an input signal
current from a high-resistance circuit to a low-resistance circuit. True
or false? FALSE
d. The ‘science of miniaturization’ involves a good understanding of the
intended application, scaling laws, different manufacturing methods
and materials. True or false? TRUE
e. Some reasons for MEMS and NEMS are:
i. Redundancy and arrays
ii. Integration with electronics, simplifying systems (e.g., single
point vs. multipoint measurement)
iii. Reduction of power budget
iv. Faster devices
v. Narrowing the dynamic range.
Cross out the wrong reason.
f. Lithography (e.g. Si-micromachining) is excellent for obtaining large
absolute tolerances. True or false? FALSE
g. Categorize bulk micromachining in terms of
i. Serial versus batch versus continuous manufacturing methodsbatch
ii. Projected versus truly 3D -2 1/2D
iii. Additive process versus subtractive process-subtractive
iv. Top-down versus bottom-up-top down-top-down
2. Lithography and LIGA
a. Resist tone:
i. Negative:
Prints a pattern that is opposite
of the pattern
that is on the mask.
ii. Positive:
Prints a pattern that is the same as the pattern
on the mask.
True or false? TRUE
b. In Contact printing, Proximity printing, Self-alignment and Projection
printing only self-alignment does not need a lens. True or false?
FALSE
c. Above Tg the resist picks up dirt quite readily and the resist profile
gets degraded. True or false? TRUE
d. The value of n sin for an optical system is the numerical aperture, or
NA. If the value of the NA is small for a system, more orders will be
imaged, and the grating may not be resolved. True or false? FALSE
e. “Off-axis illumination” allows some of the higher order diffracted light
to be captured and hence can improve resolution (by decreasing k1).
True or false? TRUE
f. Phase shift masks change the phase of light by 90° in adjacent
patterns leading to destructive interference rather than constructive
interference. True or false? FALSE
g. LIGA stands for lithography, electroplating and molding. True or false?
TRUE
h. The optimum wavelength for optimum pattern transfer in LIGA is 0.2
to 0.3 µm. True or false? FALSE
i. Diffraction increases as wavelength increases and secondary electron
emission decreases as the wavelength decreases. True or false? FALSE
3. Wet bulk micromachining
a. Proper alignment of the mask with the 110 wafer flat leads to a etch
pit with {111} sidewalls, (100) bottom, <110> directed edges and
<211> directed ribs. True or false? TRUE
b. There are {100} planes perpendicular to the wafer surface at a 45°
angle with the wafer. True or false? TRUE
c. KOH etching is very sensitive to stirring and etching bath
temperature. True or false? FALSE
d. Three types of etch stops are: epilayer with a high level of p-type
doping, p-type implantation and sacrificial oxide layer. True or false?
TRUE
4. Dry etching
a. Within a dry etching reaction chamber the wafers lie directly in the
plasma glow (also called a discharge), where ions are accelerated
towards the wafer (often biased). The ions are not doing the real
etching that is done by reactive neutrals in the plasma. True or false?
TRUE
b. In the viscous flow regime gas density (pressure) is high with many
molecule/molecule collisions (one molecule “pushes” another).
Collisions with walls play a secondary role in limiting the gas flow.
True or false? TRUE
c. In a DC plasma the asymmetry of the voltage distribution is due to the
fact that electrons move faster away from the cathode than positive
ions are accelerated towards. True or false? TRUE
d. Some conclusions based on the Paschen curve are:
i. The equivalency of pressure and distance
ii. The passion of Christ was very severe at close distances
iii. Putting electrodes very close together (< 5 µm) is equivalent to
creating a lower pressure
iv. Bringing the electrodes too close together extinguishes the
plasma
Cross out the wrong statement