= 0+1866XLO

1)

a) A bare Si wafer is oxidized in dry O2 at 1100 °C. The desired final thickness is 50 nm.

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i) Find the time required to perform the oxidation, ignoring rapid growth.

ii) Find the time required to perform the oxidation, taking rapid growth into account.

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Use Deal-Grove equations - do NOT use oxide growth curves.

b) A <111> silicon wafer is oxidised using the following sequence

i) 60 mins @ 1000°C in dry O₂.

ATB

0,065

[10 1/3 marks]

ii) 60 mins @ 1000°C in steam.

0.125

iii) Locally etch 0.1 microns of oxide to create a trench.

iv) 30 mins @ 1100°C in dry O2.

0.009

Use growth curves to calculate the oxide thickness after each step.

[10 marks

c) It is possible to determine the thickness of oxide on oxidised wafers by visual

inspection. Describe the method and discuss TWO disadvantages of this technique.

[5 marks]

d) Discuss FIVE of the features of SiO₂ which account for its widespread use in

microelectronics.

Breack down $h field

[5 marks

e) Dry oxidation is much slower than wet oxidation. Discuss briefly any advantages to

using dry oxides instead of wet oxides.

[3 mark

-Excellent stable Passivation

Excellent and stable Eelectricat Properties

If the wet wild is s is day,