【Semiconductor etching process】The soul of semiconductors teaches the etching process and the practice of engineers on defective rate problems from 0 to 1(CH9-CH10)

CH9. Wet etching process

Wet etching - mainly using the time etch method

How it works

The wafer is immersed in an etch solution or the etch solution is sprayed onto the wafer

It is widely used due to its low cost and ease of operation

Improves uniformity by heating or stirring

Etching fluids with high selection ratios are required

0021-35922 Chamber Body, Txz Mcvd

Wet etching has three stages: transport (supply), →reaction→ by-product removal (stripping) – the solution needs to be changed periodically

Mechanism

The etch fluid moves to the wafer surface by diffusion

Chemical reactions occur on the surface

By-products from etching are removed by diffusion

It is mainly used to etch oxide films, nitride films, metal films, etc

Problem

Etching at the bottom of the photoresist (PR) results in under-cuts, which has an impact on high integration

Incomplete etching

Excessive etching and excessive under-cutting

The resistor is lifted

Produces a large amount of chemical waste liquid

Pros and cons

Advantages: Batch processing / selection is better than excellent / reliability

Disadvantages: isotropic etching / large pattern size / safety issues in chemical solution treatment / need to be replaced regularly

Applications:

Surface treatment during wafer processing

Pre-treatment before thermal oxidation (for removal of organic contaminants and metal impurities)

Selective removal or stripping process for semiconductor films

Wet etching characteristics of oxide film

Etching by HF

Etching by buffered HF (BOE) (diluted with distilled water)

Reasons for adding NH₄F to BOE: Ensure a stable etch rate

Etch rate sequence: CVD oxide film > thermal oxide film

Oxide film with high concentration of impurities > Oxide film with low concentration of impurities

Wet etching characteristics of monocrystalline silicon and polysilicon

Isotropic Si etching

Solution: a mixture of nitric acid (HNO₃, silicon oxide) + hydrofluoric acid (HF, removing the oxide film formed).

Anisotropic Si etching

Solution: KOH, EDP mixture, TMAH

Although it is a wet etching, anisotropic etching can also be achieved depending on the growth surface

Wet etching characteristics of nitride films (non-important)

High temperature phosphoric acid solution / high selection ratio for oxide film

Wet etching characteristics of metals (non-important)

Aluminum: Use a heated mixed solution

Titanium: After the Self Aligned TiS₂ process, unbound areas of Ti are removed with a mixed solution

 

CH10. Etching defect cases and etching engineer practice

Dry etching defect cases

1)The etch rate within the wafer is uneven

Reason: Chuck temperature uniformity, gas flow, pressure, etc. are all influencing factors

2)The figure collapses

3)Bridging caused by the mask plate

By recreating masks (Revision) or local repairs (zapping)

4)Graphic offset caused by particles

Others:scratch, particle etc

6) Contact not Open

Phenomenon: etch not open / cause : particle

7) TSV ( through Si Via )

Phenomenon: contact etch depth abnormal / countermeasure： metal hard mask & air flow rate correct

8) High aspect ratio contact etch issue

Phenomenon：Bowing/ Mask Erosion/ Twisting

Cause: Distortion caused by deposition/high-energy electrons caused by electric fields

Solution: Increased high-energy electron flux → neutralization (trench bottom and sidewalls)

9)Under-engraving (in Bosch etching)

Bosch etching = accumulation of inhibitor, removal by ion bombardment, and stacking of inhibitor layer again, etch in this cycle

Solution: Reduce total cycle time while keeping the etch/deposition time ratio constant

Too high etch rate is the main cause of undercut → but if the underscore is reduced excessively, the etch rate will decrease

10)Footing(Lateral Undercut)

Under-marking due to cations building up at the bottom → "Footing"

11) Patterning defect ( metal blocked etch )

Cause: Poor etching mask formation (e.g., ADI pattern defects, particles, etc.)

Open defect

cause : etch margin insufficient, blockedparticle

• Wet Etch Bad Things

1) Polymer residue

2) Pinhole defect

Etch engineer

Field of work: Process engineer/equipment engineer

2)Process Engineer Role: Research and develop process manufacturing techniques/analysis and improve yields

3)Equipment Engineer Role: Equipment maintenance → Improve equipment operation rate → Improve production efficiency