I originally planned to write about deposition, but I decided to focus on the cleaning process first. The photolithography, etching, and cleaning processes are said to be incredibly challenging.
Cleaning is the process of removing particles, organic contaminants, or metallic impurities from the wafer surface. This is a crucial process, as it reduces chip defects.
Cleaning Types
Wet cleaning
Most wet cleaning methods are based on the RCA method, introduced in the 1970s. This method uses a hydrogen peroxide solution as its base, and comes in two methods: SC-1 and SC-2.
SC-1 cleaning using a basic solution, also known as APM (Ammonia Peroxide Mixture), is easy to remove organic matter and particles because it cleans through oxidation and etching reactions.
SC-2 cleaning using an acid solution, also known as HPM (Hydrochloric Acid and Peroxide Mixture), is effective in removing metal impurities.
Other cleaning methods include Piranha cleaning using sulfuric acid, DHF cleaning using HF, and ozone cleaning.
Dry cleaning
Dry cleaning reduces waste by eliminating the use of solutions, and it overcomes the drawback of wet cleaning, which cannot be used on fine patterns due to surface tension. Furthermore, because it is performed in a vacuum environment, the cleaning process can be connected to deposition or etching equipment that also operates in a vacuum environment. This has the advantage of preventing wafer contamination.
However, heavy metals have the disadvantages of being difficult to remove through chemical reactions with gas, low process reproducibility, and slow process speed.
Dry cleaning methods currently being developed include HF vapor cleaning (removal of oxide films), UV/O3 cleaning (removal of organic films), UV/Cl2 cleaning (removal of metal impurities), and H2/O2 plasma cleaning (removal of fine organic matter).
| Wet cleaning | Dry cleaning | |
|---|---|---|
| Advantage | – Easy to wash with water after the process – The liquid used is not flammable – Various chemical solutions available – Good for both organic and inorganic removal – Relatively excellent selective removal ability – Low cost | – Less chemical solution and DI water usage – Less waste liquid discharge, easy waste liquid disposal – Full scale cluster tool process possible – Advantageous for high aspect ratio structure – Easy particle control – Safer process than wet clean process |
| Disadvantage | - Dries slow and leaves residue – Some organic matter removal effects are lower than those of organic solvents. – Most chemical solutions are toxic substances – High disposal costs – Difficult to use in vacuum systems | – Use of expensive equipment – Difficult to control heavy metals or transition metals – Generally single-wafer process – When using high-temperature processes, there is a possibility of diffusion of metal impurities. |
References: SK hynix Newsroom
