Deposition (CVD and PVD)

In PVD such as sputtering and evaporation, why is it hard to coat the sidewalls and bottoms of deep trenches?

  1. ABecause atoms move to avoid trenches in PVD
  2. BBecause atoms travel almost in straight lines, they have difficulty reaching areas not in line of sight from the opening
  3. CBecause the film becomes liquid in PVD
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Answer: B. Because atoms travel almost in straight lines, they have difficulty reaching areas not in line of sight from the opening

In PVD, atoms leaving the target or evaporation source travel nearly straight and stick to the substrate. Film therefore forms readily on top surfaces and openings but has difficulty reaching areas with poor line of sight, such as trench sidewalls and bottoms. CVD and ALD, which deposit by surface chemical reactions, give better step coverage.

  • A. Atoms do not move to avoid trenches.
  • B. Correct. Straight-line travel makes it hard to reach areas out of sight.
  • C. PVD films do not become liquid.
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More Deposition (CVD and PVD) questions

  1. What is it called when a gas containing a dopant such as phosphorus is flowed during LPCVD polysilicon deposition to make a conductive film?
  2. Before filling contact holes with tungsten by CVD, what is the main reason a thin film such as TiN (titanium nitride) is deposited underneath?
  3. What is the main purpose of "densification", a high-temperature anneal after depositing oxide by low-temperature CVD or similar?
  4. In ALD, what is the temperature range called in which self-limiting surface reactions keep the thickness per cycle constant?
  5. Which is an advantage of sputtering over vacuum evaporation?