Etching

Learn the basics of etching — anisotropic etching, selectivity and the differences between wet and dry etching — through multiple-choice questions.

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Etching: key points

Etching removes the parts of a film not covered by a mask such as resist to form patterns. There is wet etching, which uses chemical solutions, and dry etching, which uses plasma and similar means.

To process fine patterns accurately, anisotropy (etching only vertically) and selectivity (etching only the target film) are important. Reactive ion etching (RIE) is a representative technique.

All Etching questions (50)

  1. Which correctly describes anisotropic etching?
  2. Which correctly describes 'selectivity' in etching?
  3. Which is a general characteristic of wet etching?
  4. Which correctly describes reactive ion etching (RIE)?
  5. Which method is commonly used to detect the endpoint of dry etching?
  6. What is the aspect ratio of a hole or trench formed by etching?
  7. What is the phenomenon called in which the etch rate decreases as patterns become narrower and deeper?
  8. Which gases are commonly used for dry etching of polysilicon gates?
  9. What is the process called that removes photoresist by oxidizing it to ash with oxygen plasma or similar?
  10. Which is a characteristic of atomic layer etching (ALE)?
  11. Which correctly describes one mechanism by which dry etching achieves anisotropy?
  12. Which solution is commonly used for wet etching of silicon nitride?
  13. During plasma etching, what is the phenomenon called in which conductors acting as antennas, such as long wires, collect charge and damage the gate oxide they connect to?
  14. Which is a characteristic of wet etching of silicon with potassium hydroxide (KOH) solution?
  15. Which is a characteristic of inductively coupled plasma (ICP) etching equipment?
  16. Which metric indicates how small the variation in etch rate is across the wafer?
  17. After the etch endpoint is detected, what is it called to continue etching for a set time to ensure the film is removed across the whole wafer?
  18. What is a mask of nitride, carbon or similar material called, used when photoresist alone cannot survive as a mask, such as when etching deep holes?
  19. Which is a characteristic of downstream etching, which supplies only plasma-generated radicals to the wafer?
  20. Which are examples of profile defects seen in high-aspect-ratio etching?
  21. If the oxide etch rate is 100 nm/min and the mask is consumed at 20 nm/min, what is the selectivity to the mask?
  22. Which solution, made by buffering hydrofluoric acid with ammonium fluoride, is used for wet etching of SiO2?
  23. Why is cryogenic etching, which cools the wafer to very low temperatures, attracting attention for high-aspect-ratio processing?
  24. Because changes in the condition of an etch chamber's walls alter results, what is it called to process dummy wafers before product to stabilize the chamber?
  25. What is an advantage of pulsed plasma, which etches while switching the RF power on and off?
  26. Which gases are commonly used for dry etching of GaN?
  27. Why is it difficult to pattern copper wiring directly by dry etching?
  28. In gate etching, what is the phenomenon called in which the pattern sidewall is undercut laterally near the boundary with the underlying insulator?
  29. Why are reaction products (polymers) left on pattern sidewalls removed after dry etching?
  30. What is needed to etch oxide and stop on the nitride underneath?
  31. What is the role of etching in semiconductor manufacturing?
  32. Which correctly describes the "plasma" used in dry etching?
  33. If etching proceeds at 100 nm/min for 3 minutes, how much film is removed?
  34. In wet etching, how does the etch rate generally change when the solution temperature is raised?
  35. In plasma tools such as capacitively coupled ones, what is the phenomenon called in which the wafer-side electrode naturally acquires a negative DC potential that accelerates ions toward the wafer?
  36. What is the masking scheme called that stacks three layers, an organic (carbon) film at the bottom, a silicon-containing middle layer and resist on top, to etch fine patterns deeply?
  37. Which gas can etch silicon isotropically without a plasma, for example to remove sacrificial layers in MEMS?
  38. Which technique gradually thins an exposed resist pattern with plasma to create lines narrower than the exposure limit?
  39. In gate electrode etching, what is commonly done to preserve the thin gate insulator underneath?
  40. When a 1 µm film is etched just down to the underlayer by perfectly isotropic wet etching, roughly how much is etched laterally from the mask edge (undercut)?
  41. Which metric expresses how far the sidewall of an etched hole or trench tilts from vertical?
  42. What is the general effect of adding a little oxygen to fluorine-based etching gas?
  43. In a typical etching plasma, how do the numbers of ions and radicals compare?
  44. Which method inserts a small electrode into a plasma and measures the current as the voltage is varied to determine the plasma's electron temperature and density?
  45. In dry etching, what is the profile defect called in which the bottom of a trench is etched deeper near the sidewalls than in the center, creating narrow grooves?
  46. Exposing silicon to XeF2 gas and an argon ion beam simultaneously etches it far faster than the sum of either alone. What property of dry etching does this show?
  47. In plasma etching of high-aspect-ratio patterns, which phenomenon has electrons blocked by sidewalls so negative charge builds at the top of the pattern while positive ions are deflected at the bottom, causing profile defects and damage?
  48. Which research-stage etching method neutralizes plasma-generated ions before they hit the wafer, suppressing charging and UV damage?
  49. Why are coatings such as yttrium oxide (Y2O3) used on the inner walls and parts of plasma etch tools?
  50. In plasma etch tools, what is the main role of the focus ring surrounding the wafer edge?

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