Term
| When do the Darken relations apply? When do you use the Nernst-Plank relations? |
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Definition
Darken:
-When there is an efficient operation of sources and sinks for vacancies
- when diffusion is sufficiently slow that stresses resulting from any volume changes can be effectively relaxed
Nernst-Planck:
not efficient sinks for vacancies, porosuty, short diffusion distances |
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Term
| What drives diffusion in an ideal solution? |
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Definition
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Term
| What can you get if the enthalpy of mixing is fairly large and positive? |
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Definition
| uphill diffusion and spinodal decomposition |
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Term
| Give examples of elements that diffuse fast interstitially through Si. |
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Definition
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Term
| What effect does diffusion of Au in Silicon display and why? |
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Definition
| Frank-Turnbull mechanism- this results in a symmetric diffusion profile which results from the fact that Au can diffuse both interstially and substitutionally in Si. Interstitial diffusion is much faster than substitutional diffusion, so you see Au at the other end due to interstitial diffusion of Au and Silicon vacancy diffusion. |
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Term
| Give one problem with using pure Al metallizations in Si? What is the solution. |
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Definition
| Si diffuses out into the Al and you get AL spikes in the device. If you supersaturate the Al with Si by adding 1wt% Si you can solve this problem |
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Term
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Definition
| cat ion moves to an interstitial site and creates a vacancy |
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Term
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Definition
| vacancies on anion and cation sites are balanced to ensure neutrality |
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Term
| Give examples of n-type and p-type oxides. |
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Definition
n-type ZnO: excess e-
n-type: TiO2- anion deficiency
p-type: Nio- metal defecit |
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Term
| What do you need for oxide growth? |
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Definition
| ionic conductivity and electronic conductivity |
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Term
| What are the important forces involved in electromigration |
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Definition
1) direct Force which arises because of the charge of metal ions
2)wind force which arises due to the momentum transfer from electrons to metal ions |
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Term
| What is the effective charge? what influences its charge and magnitude? |
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Definition
the effective charge is the charge that you can treat metal ions as having due to their behavior in an electric field due to electromigration.
-low resistance metals usually have negative z* electron wind dominates |
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Term
| What is the overall effect of current densities in metal conductors |
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Definition
| they cause a slight biasing of the diffusional jumps of atoms |
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Term
| Why is electromigration significant in ICs? |
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Definition
| high j due to the smallness of ICs typically < .18microns wide |
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Term
| What kinds of damage can you get in ICs due to electromigration? |
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Definition
| voids; hillocks and whiskers |
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Term
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Definition
| when atoms respond to a gradient in hydrostatic pressure |
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Term
| What are the criteria for damage due to mechanodiffusion? |
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Definition
you get no damage if:
L< (jL)crit/j
or
j < (jL)crit/L |
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Term
| What is the dominant capacitance in modern devices due to? |
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Definition
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Term
| What are the advantages of using Cu lines over Al? disadvantages? |
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Definition
advantages:
- Cu has a better conductivity
- slower bulk transport in Cu -> less worry with creep, etc.
- surface transport -> don't have to worry about grain structure
-better conductivity
-stronger
disadvantages:
- Al is inert but CU must be isolated from SiO2
-worse corrosion resistance |
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Term
| The thermal expansion of a liquid is ____ than that of the corresponding crystal |
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Definition
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Term
| When does the glass transition occur in relation to viscosity? |
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Definition
| When the viscosity becomes so high that it prevents structural changes from keeping pace with the cooling rate. |
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Term
| What are some predictions of the Vogel-Fulcher-Tamman equation. |
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Definition
any liquid will form a glass if crystallization can be suppressed
- some free volume is always frozen in at the glass transition |
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Term
| Grain growth in metals is significant for what temperatures? |
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Definition
| T> .5 (melting point temperature) |
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Term
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Definition
average grain size increases with time
- self-similar growth |
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Term
| What grains tend to grow? diminish? why? |
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Definition
| more than six sides grow, less than six sides diminish, due to curvature resulting in grains with more sides having a lower free energy. |
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Term
| When does abnormal grain growth occur? |
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Definition
| when some grains or crystallographic orientations are favored due to lower elastic energies or lower surface energies |
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Term
| Give mechanisms for pinning of grain boundaries? |
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Definition
| zener drag and thermal grooving |
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Term
| what structure do you expect narrow IC lines to achieve? WHy? |
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Definition
| bamboo structure, because no curvature therefore no further driving force for grain growth |
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Term
| diffusion limited interface velocity. give typical speeds |
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Definition
| the atomic motion at the solid-liquid interface during solidification is similar to the jumps necessary for diffusion in the liquid. Therefore, diffusion limits the speed. typical speeds would be around 10 m/s |
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Term
| collision limited interface velocity. give typical speeds |
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Definition
| solidification in this instance occurs so quickly that atoms just shuffle into place; speeds of 1000m/s |
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Term
| What is solute trapping?Why is it important? |
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Definition
| this occurs when the interface velocity is sufficiently high- can determine iff sufficiently high using the partition coefficient.used in ion implantation . Ion implantation is necessary for some dopants that cannot be diffused in because they have very low equilibrium solubilities in Si. implantation however damages the Si(amorphizes Si), so you need to regrow the Si rapidly. |
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Term
| What is ostwaldt ripening? What is the driving force?What is the rate of coarsening proportional to? |
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Definition
| coarsening of precipitate distributions- driving force is curvature r is proportional to t^(1/3) |
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Term
| What does the order parameter say? |
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Definition
rho = 1/2 perfectly random
rho = 0,1 ordered |
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