Plasma Etching


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Plasma Etching

  1. 1. Plasma Etching By Student : EE576 (VLSI Processing) Minh Anh Thi Nguyen 11/8/01
  2. 2. Outline <ul><li>What is plasma Etching </li></ul><ul><li>Parameters in plasma </li></ul><ul><li>Isotropic and Anisotropic </li></ul><ul><li>Types of plasma etching system </li></ul><ul><li>Reactive plasma etching and equipment </li></ul><ul><li>Processes of plasma etching </li></ul><ul><li>Advantages and disadvantages of plasma etching </li></ul><ul><li>How plasma etching works </li></ul><ul><li>Why use plasma etching </li></ul>
  3. 3. When Plasma Etching applies in Microelectronic <ul><li>By the early 1970s, plasma etching was first widely adapted to device manufacturing, which was mainly oxygen plasma. At this time, it was primarily used for photo resist ashing. </li></ul><ul><li>By the late 1970s, it was widely recognized that plasma etching can offer the possibility of anisotropy etching, then rapidly increasing microelectronic industry drives the transition from wet etching to plasma etching and continuously promotes its development. </li></ul>
  4. 4. What is Plasma Etching <ul><li>Also known as dry etching </li></ul><ul><li>One of the most important processes in IC manufacturing </li></ul><ul><li>A key process for removing material from surface </li></ul><ul><li>has a number of advantage over chemical etching </li></ul><ul><li>uses a gas that is subjected to an intense electric field </li></ul><ul><li>the only commercially usable technology for anisotropy removal of material from surface </li></ul>
  5. 5. Types of plasma etching system <ul><li>None plasma based </li></ul><ul><li>uses spontaneous reaction to appropriate reactive gas mixture </li></ul><ul><li>2. Plasma based </li></ul><ul><li>uses radio frequency (RF) power to drive chemical reaction </li></ul>
  6. 6. None plasma based <ul><li>Isotropic etching of silicon </li></ul><ul><li>Typically fluorine-containing gases (interhalogens) that is readily to etch si </li></ul><ul><li>Highly selectivity making layers </li></ul><ul><li>No need processing plasma equipment </li></ul>
  7. 7. Plasma based <ul><li>RF power is used to drive chemical reactive </li></ul><ul><li>Plasma takes place of elevated temperature or very reactive chemicals </li></ul>
  8. 8. Isotropic etching <ul><li>A process that etches at the same rate in all direction </li></ul><ul><li>Very good pattern transfer </li></ul><ul><li>Poor selectivity </li></ul><ul><li>Can etch anything </li></ul><ul><li>High etch rate </li></ul>
  9. 9. Anisotropic etching <ul><li>A process that etches only in one direction. </li></ul><ul><li>Preferable for smaller feature dimension </li></ul>
  10. 10. Isotropic Vs. Anisotropic <ul><li>Isotropic: vertical and horizontal </li></ul><ul><li>Anisotropy: much higher vertical rate than horizontal </li></ul><ul><li>Isotropic Anisotropic </li></ul>
  11. 11. Isotropic vs. Anisotropic <ul><li>hf = thickness of the thin film </li></ul><ul><li>l= lateral distance etched underneath </li></ul><ul><li>Af = degree of anisotropic </li></ul><ul><li>Af = 1- l/hf </li></ul><ul><ul><li>Anisotropic </li></ul></ul><ul><li>Af = degree of isotropic </li></ul><ul><li>hf = l </li></ul><ul><li>Af = 0 </li></ul><ul><li>isotropic </li></ul>
  12. 12. Plasma etching <ul><li>There are five classes of plasma etching mechanisms </li></ul><ul><ul><li>Sputter etching </li></ul></ul><ul><ul><li>Chemical etching </li></ul></ul><ul><ul><li>Accelerated ion-assisted etching </li></ul></ul><ul><ul><li>Sidewall-protected ion-assisted etching </li></ul></ul><ul><ul><li>Reactive ion etching (RIE) </li></ul></ul>
  13. 13. Sputter etching <ul><li>Highly anisotropic </li></ul><ul><li>A purely physical process </li></ul><ul><li>Very similar to ion implantation but low energy ions are used to avoid implantation damage </li></ul>
  14. 14. Chemical etching <ul><li>isotropic </li></ul><ul><li>Plasma is used to produce chemically reactive species (atoms radical and ions) from inert molecular gas. </li></ul><ul><li>Production of gas by products is extremely important </li></ul>
  15. 15. Accelerated ion –assisted etching <ul><li>Like the sputter etching ions are accelerated by the sheath potential </li></ul>
  16. 16. Sidewall-protected ion-assisted etching <ul><li>Can be anisotropic </li></ul><ul><li>Involves additional species to create a protective sidewall barrier. </li></ul>
  17. 17. Reactive ion etching <ul><li>Process in which chemical etching is accompanied by no undercutting since side-wall are not exposed (ie. Ion assisted etching) </li></ul><ul><li>Bombardment opens areas for reactions </li></ul><ul><li>Low selectivity </li></ul>
  18. 18. Parameters in plasma <ul><li>Temperatures: etching rate and directivity </li></ul><ul><li>Pressure: ion density and ion directivity </li></ul><ul><li>Densities :charged and neutral particles </li></ul><ul><li>Power: ion density and ion kinetic energy </li></ul><ul><li>Other variable: gas flow rate, loading, reactor material and masking material </li></ul>
  19. 19. Plasma etch process temperature control <ul><li>Process temperature is the single most important parameter in the plasma process. </li></ul><ul><li>Process temperature has primary control over etch rate and has a secondary effect on etch uniformity </li></ul><ul><li>the temperature at which the process operates has a major influence on processing rates. </li></ul>
  20. 20. Plasma temperature control (cont.) <ul><li>The higher the process temperature, the faster the processing rate. </li></ul><ul><li>Process temperature control is mandatory when processing temperature sensitive devices. </li></ul><ul><li>Uncontrolled process temperature can cause distortion. </li></ul>
  21. 21. Low pressure <ul><li>-To help etching by product diffuse out the via </li></ul><ul><li>- The mean free path lengths of gas molecules and ion are longer and this reduces scattering collision that can cause a loss in profile control </li></ul>
  22. 22. How Plasma etching works <ul><li>Chamber is evacuated </li></ul><ul><li>Chamber is filled </li></ul><ul><li>with gases </li></ul><ul><li>RF energy is </li></ul><ul><li>applied to pair </li></ul><ul><li>of electrodes </li></ul>
  23. 23. How Plasma etching works <ul><li>Applied energy accelerates electron increasing kinetic energy </li></ul><ul><li>Electron collide with neutral gas molecules forming ions and more electrons </li></ul><ul><li>Plasma discharge is bulk region and dark or sheath region near electrodes </li></ul><ul><li>Bulk region is semi-neutral or nearly equal to number of electrons and ions </li></ul><ul><li>Sheath region is nearly all of the potential drop; accelerates “+” ions from bulk region which bombard the substrate </li></ul><ul><li>Maintained at 1 Pa(75mtorr) to 750 Pa (56torr) with gas density of 27x10 ˆ14 to 2x 10^17 molecules / cm^3 </li></ul>
  24. 24. Reactive plasma etching and equipment <ul><li>Barrel reactor </li></ul><ul><li>Reactive Ion Etcher (RIE) </li></ul><ul><li>Magnetic-Enhanced RIE (MRIE) </li></ul><ul><li>electron cyclotron resonance plasma etcher (ECR) </li></ul><ul><li>inductively coupled plasma (ICP) </li></ul><ul><li>Clustered plasma processing </li></ul>
  25. 25. Barrel Reactor <ul><li>The main components of the barrel reactor is the cylindrical vacuum chamber with a pair of RF electrodes concentrically inside </li></ul>
  26. 26. RIE system <ul><li>Asymmetrical parallel plate system </li></ul><ul><li>Plasma, sheath and boundary layer </li></ul><ul><li>Combination physical and chemical etching </li></ul><ul><li>Advantage: Anisotropy etching </li></ul><ul><li>Disadvantage: </li></ul><ul><li>low etch rate </li></ul><ul><li>low selectivity </li></ul><ul><li>Surface damage </li></ul>
  27. 27. MRIE system <ul><li>Advantage: </li></ul><ul><li>large anisotropic </li></ul><ul><li>high etch rate </li></ul><ul><li>reduced surface damage </li></ul><ul><li>etching relative independent of loading </li></ul>
  28. 28. ERC system <ul><li>Higher plasma density at low pressure </li></ul><ul><li>Control the density of </li></ul><ul><li>reactive ion and their </li></ul><ul><li>kinetic energy separated </li></ul>
  29. 29. ICP system <ul><li>Simple system </li></ul><ul><li>Almost same process </li></ul><ul><li>result as that from </li></ul><ul><li>ERC system </li></ul><ul><li>Two RF power </li></ul><ul><li>generators to control </li></ul><ul><li>ion energy and ion </li></ul><ul><li>density separately </li></ul>
  30. 30. Clustered plasma system <ul><li>Use a wafer handle to pass wafers from one process chamber to another in a vacuum environment </li></ul><ul><li>can also increase throughput, and provide an advantage of high chip yield, since wafer is exposed to less contamination. </li></ul><ul><li>minimize particulate contamination </li></ul>
  31. 31. Processes of plasma etching
  32. 32. Advantages of Plasma etching <ul><li>Easy to control and reproduce </li></ul><ul><li>Operated in low pressure chamber </li></ul><ul><li>No liquid waste </li></ul><ul><li>Uses small amounts of chemicals </li></ul><ul><li>Eliminates handling of dangerous acids </li></ul><ul><li>can be highly selective to underlying layers </li></ul><ul><li>causes little damage to the photo resist </li></ul>
  33. 33. Disadvantages of plasma etching <ul><li>the wafer can be damaged from the RF radiation. </li></ul><ul><li>Tendency for isotropic etching </li></ul><ul><li>poor pattern transfer </li></ul><ul><li>Some gases are quite toxic </li></ul><ul><li>Expensive equipment </li></ul>
  34. 34. When do we want to use plasma etching <ul><li>The first thing you should note about this technology is that it is expensive to run compared to wet etching. </li></ul><ul><li>Need vertical side walls for deep etching in the substrate </li></ul><ul><li>Adopted plasma etching to achieve small features </li></ul>
  35. 35. Why use plasma etching? <ul><li>Fast </li></ul><ul><li>Selective </li></ul><ul><li>Low damage </li></ul><ul><li>Anisotropic </li></ul>
  36. 36. References <ul><li>Glow Discharge Processes </li></ul><ul><li> </li></ul><ul><li>An introduction to plasma etching for VLSI circuit technology </li></ul><ul><li>Plasma etching processes for ULSI semiconductor circuits </li></ul>
  37. 37. <ul><li>Thank You </li></ul>