Term
| Oxidation occurs at the Si/SiO2 (native oxide) interface. Name two benefits of this. |
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Definition
1. The growing SiO2 layer has not seen atmosphere
2. The grown oxide is relatively free of impurities. |
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Term
| During the oxidation process, the thickness of Si consumed is how many times the oxide thickness? |
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Definition
| The thickness of Si consumed is ~0.45x the oxide thickness. |
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Term
| What are the two techniques for silicon oxidation? |
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Definition
1. Dry oxidation
2. Wet oxidation |
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Term
| The Deal-Grove Model of Oxide Growth Rate is severely inaccurate for oxides less than __ nm? |
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Definition
| It is severely inaccurate for oxides less than 30 nm thick. |
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Term
Does oxide grow faster on <111> Si or <100> Si? Why?
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Definition
| Oxide grows faster on <111> Si because there are more Si atoms on the plane. |
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Term
| Name 2 common ways of measuring oxide thickness. |
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Definition
Any of the following:
1. Etching a hole in the oxide and physically measuring the height (but this is destructive).
2. Using optical interference techniques (Nanospec)
3. Observing the color of the oxide |
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Term
| What is the segregation coefficient 'm' when referring to dopant redistribution? |
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Definition
The ratio of thermal-equilibirum dopant concentrations in SiO2 versus Si.
m = concentration of impurity in Si/concentration of impurity in SiO2 |
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Term
| Name the four types of detrimental charges that can be present in an oxide. |
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Definition
1. Fixed Oxide Charge
2. Mobile Ionic Charge
3. Interface Trapped Charge
4. Oxide Trapped Charge |
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Term
| What causes fixed oxide charge present at the Si/SiO2 interface? |
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Definition
| Fixed oxide charge is caused by a thin transition region at the Si surface formed by Si atoms that have not fully oxidized. |
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Term
| How can you decrease the occurance of fixed oxide charge? |
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Definition
| Fixed oxide charge can be decreased by a high temperature anneal in an inert atmosphere (Ar, N2) after oxidation. |
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Term
| What is the most common ion causing Mobile Ion Charge? |
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Definition
| Na-. K+ and Li+ also occur. |
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Term
| What do Interface Trapped Charges at the Si-SiO2 affect? |
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Definition
| Interface Trapped Charges affect threshold voltage and reduce carrier mobility. |
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Term
| What causes Oxide Trapped Charge? How can it be avoided? |
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Definition
| Oxide Trapped Charge is caused by electrons or holes trapped in the oxide due to ionizing radiation. It can be reduced by low temperature annealing. |
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Term
| Why is it desirable to avoid temperature ramp-up and ramp-down when heating wafers? |
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Definition
| Temperature ramp-up and ramp-down time can cause dopant redistribution in the wafer. |
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Term
| When do we want to use Rapid Thermal Oxidation (RTO) as an oxidation process? |
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Definition
| To grow very thin films. It is undesirable to use low temperatures (increases charge faults), but high temperature ramping can cause dopant redistribution. |
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