Exam 2 Flashcards
Crystal defects
1) interstitial impurity atom
2) edge dislocation
3) silicon self-interstitial
4) coherent precipitate of substitutional atoms
8) vacancy
9) large substitutional atom compressing the lattice
What condition will result in the formation of extrinsic stacking fault by insertion of an extra partial plane in the stacking order
The sequence around the extrinsic fault is …ABCBABC…, where B at the center is the extra plane. close-packing is preserved, so that no nearest-neighbor bonds are disturbed. There are, however, irregularities in the second-neighbor relations across the fault, two for both I and E.
Name a benefit of having oxygen in the CZ-grown crystal.
Oxygen acts as a gettering agent for trace metal impurities in the crystal and it can pin dislocations which greatly strengthens the crystal. Oxygen precipitates in the wafer core suppress stacking faults, and oxygen makes the Si more resistant to thermal stress during processing.
If dopant clusters formed due to excess concentration, would the resistivity of the material increase or decrease?
More dopant, less resistivity
add mobile electrons or holes to the material, so higher concentration gives you higher conductivity (and lower resistivity).
If a rapid-thermal process results in non-uniform wafer heating and cooling, what might happen to the crystal as a response to the buildup of stress?
microcracks at the edges of the wafers
curvature
How was precipitate formation avoided in the surface region?
The surface region must be depleted of oxygen (denuded zone) using thermal annealing to lower the oxygen concentration below 15ppm, or 7.5x1017cm-3
What benefit does intrinsic gettering provide?
forms defect regions that are thermally stable at high temperature
gettering region closer to the device region than the back of the wafer is much more effective at trapping contaminants that are moving in random fashion due to thermal energy
There are no hole carriers in n-type silicon.
T/F
F, hole carrier is a minority
As temp rises, material becomes more
intrinsic
doping increases, mobility ______
decreases
Electron and hole concentrations can both be increased in the same piece ofmaterial if both donor and acceptor ions are added
T/F
F
At room temperature the intrinsic carrier concentration is negligible for any practical calculation of majority carriers in doped silicon
T/F
T
Provide the specific ion species (mass & charge state) and energy used for the PMOS implant
B pos chage ion
bf3
energy 50 kev
Why is the beamline under vacuum?
The beamline evacuated to a high vacuum so there are few gas molecules in the path for the beam of accelerated particles to hit, which otherwise could scatter them before they reach their destination.
Optimize ion implant
X scan “M” and the Y scan “M
