CMP and cleaning

Check planarization by CMP, dishing, and the purposes of RCA cleaning (SC-1 and SC-2) with multiple-choice questions.

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CMP and cleaning: key points

CMP (chemical mechanical polishing) planarizes the wafer surface by combining the chemical action of a slurry with mechanical polishing by a pad. It is essential for multilevel interconnects and for forming copper wiring by the damascene process.

Cleaning removes particles, organics, metal contamination and native oxide, and is repeated many times during manufacturing. Learn how the chemicals derived from RCA cleaning are used for different purposes.

All CMP and cleaning questions (50)

  1. Which correctly describes CMP (chemical mechanical polishing)?
  2. What is the main purpose of SC-1 (a mixture of ammonia and hydrogen peroxide) in RCA cleaning?
  3. Which correctly describes 'dishing' in CMP?
  4. What is the main purpose of cleaning with dilute hydrofluoric acid (DHF)?
  5. Which correctly describes the slurry used in CMP?
  6. What is the main purpose of cleaning with a mixture of sulfuric acid and hydrogen peroxide (SPM)?
  7. What in particular must be removed by cleaning after CMP?
  8. What is an advantage of single-wafer cleaning tools, which process one wafer at a time?
  9. What is the main purpose of using IPA (isopropyl alcohol) when drying wafers after cleaning?
  10. Which method is used to detect the polishing endpoint in CMP?
  11. In Preston's equation for CMP removal rate, which quantity is the removal rate proportional to?
  12. Which abrasive particles are often used in STI CMP to achieve high polishing selectivity of oxide to silicon nitride?
  13. Which cleaning method applies MHz-range ultrasound to the cleaning solution to remove tiny particles from the wafer surface?
  14. What is the main purpose of cleaning with ozone dissolved in ultrapure water (ozonated water)?
  15. What is the role of benzotriazole (BTA) and similar additives in copper CMP slurries?
  16. What is the role of the retaining ring that surrounds the wafer in a CMP polishing head?
  17. Why are particles, once detached, unlikely to redeposit in alkaline cleaning solutions such as SC-1?
  18. What problems are caused by metal contamination such as iron and copper on the wafer surface?
  19. What is the main cause of fine scratches on the wafer surface in CMP?
  20. To prevent fine structures from collapsing, which method removes native oxide and the like without using liquids?
  21. Which combination correctly lists processes in which CMP is used?
  22. What is the operation called in which the surface of a CMP pad is dressed with a diamond tool to stabilize the removal rate?
  23. Compared with planarization by thermal reflow or etch-back, what is an advantage of CMP?
  24. Which correctly describes the order and purposes of SC-1 and SC-2 in standard RCA cleaning?
  25. What is the main cause of pattern collapse when cleaning and drying high-aspect-ratio patterns?
  26. Why are oxidizers such as hydrogen peroxide added to the slurry in tungsten CMP?
  27. What is a correct design countermeasure to the CMP removal amount varying with pattern density within a chip?
  28. What is the approximate size of the abrasive particles in CMP slurries?
  29. What is the main purpose of diluting chemicals or using functional water in recent cleaning processes?
  30. What is the main purpose of cleaning the back and edge (bevel) of wafers?
  31. What is the main reason wafer cleaning is considered important in semiconductor manufacturing?
  32. Which correctly describes how many times cleaning is performed across the whole LSI manufacturing flow?
  33. Which set correctly lists the kinds of surface contamination removed from wafers by cleaning?
  34. In processes such as multilevel wiring, what is the main reason the wafer surface must be planarized by CMP?
  35. Which correctly describes the basic configuration of a CMP tool?
  36. In Cu interconnect CMP, why is polishing generally divided into stages?
  37. Which correctly describes the general difference between hard and soft CMP polishing pads?
  38. What is the state of a silicon surface whose last cleaning step was dilute hydrofluoric acid?
  39. What is the main purpose of installing filters in the lines that supply CMP slurry to the polisher?
  40. When removing particles from a wafer surface by cleaning, how does particle size generally relate to ease of removal?
  41. As CMP continues, the polishing pad temperature rises. How does the removal rate generally change?
  42. In SC-1 (a mixture of ammonia and hydrogen peroxide), what role does the hydrogen peroxide play?
  43. Which method is commonly used to count particles on a wafer surface after cleaning?
  44. Why is it considered important to transfer wafers to cleaning right after CMP while still wet, without letting them dry?
  45. What is a point of caution for batch cleaning, in which many wafers are immersed in the same tank of cleaning solution?
  46. Which cleaning method, researched and commercialized for removing particles without collapsing fine patterns, sprays tiny particles of cryogenic carbon dioxide or argon?
  47. What is the main purpose of a CMP head that can vary the pressure pressing the wafer in several concentric zones?
  48. Which CMP method fixes the abrasive particles in the polishing pad instead of putting them in the slurry?
  49. Which known problem tends to occur if rinsing after SPM (sulfuric acid and hydrogen peroxide) cleaning is insufficient?
  50. Which polishing method, studied for uses that require low mechanical force, combines electrochemical dissolution to planarize metal?

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