Deposition (CVD and PVD)

Before filling contact holes with tungsten by CVD, what is the main reason a thin film such as TiN (titanium nitride) is deposited underneath?

  1. ATo change the color of the tungsten
  2. BTo improve tungsten adhesion and protect the underlying layers from fluorine in the WF6 source
  3. CTo make the tungsten an insulator
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Answer: B. To improve tungsten adhesion and protect the underlying layers from fluorine in the WF6 source

Tungsten does not adhere well to oxide by itself, and fluorine from the source gas tungsten hexafluoride (WF6) reacts with underlying silicon or titanium and causes defects. A Ti/TiN layer is therefore laid down to act as an adhesion layer and barrier before the tungsten fill.

  • A. It is not for changing color.
  • B. Correct. It ensures adhesion and protects against fluorine.
  • C. Tungsten is used as a conductor.
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More Deposition (CVD and PVD) questions

  1. What is the main purpose of "densification", a high-temperature anneal after depositing oxide by low-temperature CVD or similar?
  2. In ALD, what is the temperature range called in which self-limiting surface reactions keep the thickness per cycle constant?
  3. Which is an advantage of sputtering over vacuum evaporation?
  4. Which type of CVD reactor heats only the stage holding the wafer while keeping the reactor walls cool?
  5. Which is an example of the precursors used to deposit HfO2 gate dielectrics by ALD?