FEOL (Front End of Line: substrate process, the first half of wafer processing)
9. Contact holes

How a semiconductor wafer is made »

To connect electrodes such as gates, sources, and drains of transistors to metal wiring layers, contact holes are made in the dielectric film and filled with W (tungsten).

Plug-tungsten filling: Tungsten is deposited in contact holes.

Plug-tungsten polishing: The surface is polished to remove excess tungsten and leave tungsten only in the contact holes.


9-1. Formation of contact hole resist pattern

A resist pattern for contact holes is formed.

9-2. Contact hole etching

Using the contact hole resist pattern as a mask, contact holes are formed in the dielectric film by performing etching treatment. After etching, the resist pattern is removed. These holes are extremely small and deep (high aspect ratio), and thus great care must be taken to control hole diameter and depth.

9-3. Plug-tungsten filling

A tungsten film is formed on the silicon wafer surface using the CVD method, and the contact holes are filled.

9-4. Plug-tungsten polishing

The surface is polished and excess tungsten film is removed. Tungsten is left only in the contact holes.

Process Flow

FEOL (Front End of Line: substrate process, the first half of wafer processing)
| 1. Isolation| 2. Well and channel formation| 3. Gate oxidation and gate formation| 4. LDD formation|
5. Side wall spacers | 6. Source/drain| 7. Silicide | 8. Dielectric film|
9. Contact holes|

BEOL (Back End of Line: interconnect process, the second half of wafer processing)
| 10. Metal-1| 11. Metal-2|

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