Silicon Production and Crystallography

Question 1

What is the base substrate of most MEMs devices?

Answer 1

single crystal silicon wafers

Question 2

Czochralski method

Answer 2

grows a single silicon crystal ingot from a molten mass and a seed crystal
- the seed crystal is inserted into molted silicon, twisted and then pulled upwards.
- doping increase at the bottom as the ratio of dopants is disturbed

Question 3

Float zone production

Answer 3

creates higher purity ingots, but is limited to a diameter of 200mm or less

Question 4

Sub aperture finishing

Answer 4

reduces height variation across a wafer, areas near the edges will have higher final height variation

Question 5

From an ingot, silicon wafers are:

Answer 5

• sliced
• lapped to remove roughness
• etched (acid baths smooth)
• polished

Question 6

Silicon exhibits these different properties across different crystal planes

Answer 6

• youngs modulus
• electron mobility
• piezo resistivity
• chemicals etch rates

Question 7

For silicon, a = ?

Answer 7

a = 5.4309Angstroms

Question 8

How to identify Miller place indices?

Answer 8

0) Identify the plane of interest
1) Identify intercepts of the plane with x, y, z axes (a, infinity..)
2) Take the reciprocal of the intercepts above
3) Reduce these #s to the smallest set of integers h, k, l by multiplying with a.

() round brackets indicate crystal plane

Question 9

Families of similar planes

Answer 9

• Are denoted with curly brace {}
• Similar planes have identical material properties

Question 10

Finding Crystal directions

Answer 10

1) Find the normal vector that begins at the origin
2) reduces the three coordinates to the smallest set of integers [h,k,l]

[] square braces denote directions

Question 11

The weakest si plane is

Answer 11

110, the primary flat plane, which is where it tends to fracture.
This is perpendicular to the 100 plane face in a 100 wafer