# Anisotropic Etching in Semiconductor Fabrication

• pj33
In summary: Etching occurs when the surface is in contact with the etchant. The Si(111) is the stable state that converges everytime (if sufficient etching time is given).
pj33
TL;DR Summary
Why does the Si(111) has low etching rate
I am learning about designing semiconductors but I had some issues understanding some things about the structure of Si.

1) Why does an FCC has 8 atoms per cell? Doesnt has 14?

1) I know you can have wafers along different surfaces. What information can I calculate for the different surfaces liek Si(101), Si(111)... and how?(is there a formula). I mean I know when etching occurs for some reason Si(111) forms a 54.7 degree angle but I don't understand why.
2)Why in anisotropic etching does the Si(111) has the lowest etching rate?
3)When etching occurs, is the Si(111) the stable state that converges everytime (if sufficient etching time is given)?

I feel that my questions above my not be that clear (for etching), but I hope with the following everything will make sense.
What does it mean to have a Si(100) wafer with sides in the <110> directions and then a groove will be etched with the sides at an angle of 54.7 degrees wrt to the surface.

Since it's a Si(100) how does it have sides of <110> direction.
Why it makes at angle of 54.7? Is this because at <111> direction is most stable and this is the corresponding angle that is formed at <111> direction?

pj33 said:
Summary:: Why does the Si(111) has low etching rate

I am learning about designing semiconductors but I had some issues understanding some things about the structure of Si.

1) Why does an FCC has 8 atoms per cell? Doesnt has 14?

1) I know you can have wafers along different surfaces. What information can I calculate for the different surfaces liek Si(101), Si(111)... and how?(is there a formula). I mean I know when etching occurs for some reason Si(111) forms a 54.7 degree angle but I don't understand why.
2)Why in anisotropic etching does the Si(111) has the lowest etching rate?
3)When etching occurs, is the Si(111) the stable state that converges everytime (if sufficient etching time is given)?

I feel that my questions above my not be that clear (for etching), but I hope with the following everything will make sense.
What does it mean to have a Si(100) wafer with sides in the <110> directions and then a groove will be etched with the sides at an angle of 54.7 degrees wrt to the surface.

Since it's a Si(100) how does it have sides of <110> direction.
Why it makes at angle of 54.7? Is this because at <111> direction is most stable and this is the corresponding angle that is formed at <111> direction?

(1) The FCC lattice has 4 atoms per unit cell, not 8 or 14. There are 6 atoms on the 6 faces, each of which is 1/2 in the unit cell, and 8 atoms at the corners, each of which is 1/8 in the unit cell, so there are 6*1/2+8*1/8=4 atoms in the unit cell.

(2) You might try watching this YouTube video:

.

It shows the various crystal planes. I think of it as follows. When you cut through the (100) plane, each atom is bonded to 4 atoms in that plane. When you cut through the (111) plane, each atom is bonded to 6 atoms in that plane. So it is more difficult for the etchant to remove atoms along the (111) plane, so the etch rate is lower. As to why the 54.7 degrees, this is just the geometry of the cubic lattice. Try calculating that angle and see what you get.

HAYAO, Borek, chemisttree and 2 others

## 1. What is anisotropic etching?

Anisotropic etching is a type of etching process used in semiconductor fabrication where the etching rate is different in different crystallographic directions, resulting in the creation of precise and controlled patterns on the surface of a semiconductor material.

## 2. How does anisotropic etching work?

Anisotropic etching works by using a chemical or plasma etchant that selectively removes material along certain crystallographic directions, while leaving other directions intact. This results in the formation of precise patterns on the surface of the semiconductor material.

## 3. What are the advantages of anisotropic etching?

The main advantage of anisotropic etching in semiconductor fabrication is its ability to create highly precise and controlled patterns on the surface of a semiconductor material. This is crucial for the production of integrated circuits and other semiconductor devices.

## 4. What are the common applications of anisotropic etching?

Anisotropic etching is commonly used in the fabrication of integrated circuits, microelectromechanical systems (MEMS), and other semiconductor devices. It is also used in the production of solar cells, sensors, and other electronic components.

## 5. What factors affect the anisotropic etching process?

The anisotropic etching process can be affected by various factors such as the type of etchant used, the composition and crystal structure of the semiconductor material, the temperature and pressure of the etching environment, and the design of the etching mask. These factors can impact the etching rate and the final pattern produced on the surface of the material.

• Materials and Chemical Engineering
Replies
1
Views
2K
• Biology and Chemistry Homework Help
Replies
4
Views
2K
• Materials and Chemical Engineering
Replies
4
Views
1K
• Engineering and Comp Sci Homework Help
Replies
2
Views
3K
Replies
1
Views
2K
• Classical Physics
Replies
19
Views
1K
• Atomic and Condensed Matter
Replies
5
Views
8K
Replies
1
Views
2K
• Atomic and Condensed Matter
Replies
1
Views
2K
• Atomic and Condensed Matter
Replies
4
Views
6K