Use of mask shadowing and angled implantation in fabricating asymmetrical field-effect transistors

{
  "publication_number": "US6566204B1",
  "country": "US",
  "kind": "B1",
  "title": "Use of mask shadowing and angled implantation in fabricating asymmetrical field-effect transistors",
  "abstract": "To furnish an IGFET (120 or 122) with an asymmetrically doped channel zone (144 or 164), a mask (212) is provided over a semiconductor body and an overlying electrically insulated gate electrode (148 P or 168 P). Ions of a semiconductor dopant species are directed toward an opening (213) in the mask from two different angular orientations along paths that originate laterally beyond opposite respective opening-defined sides of the mask. The location and shape of the opening are controlled so that largely only ions impinging from one of the angular orientations enter the intended location for the channel zone. Ions impinging from the other angular orientation are shadowed by the mask from entering the channel zone location. Although the ions impinging from this other angular orientation do not significantly dope the channel zone location, they normally enter the semiconductor body elsewhere, e.g., the intended location for the channel zone of another IGFET.",
  "claims": [
    "1. A method comprising the steps of: furnishing a gate electrode generally above, and vertically separated by gate dielectric material from, an intended channel-zone location in a semiconductor body along its upper surface; providing a mask over the semiconductor body and the gate electrode such that the mask has a mask opening which at least partially overlies the gate electrode and which defines opposite first and second transverse mask sides located laterally beyond the gate electrode and any material situated on opposite transverse sides of the gate electrode; performing one of (a) directing first ions of a species of a primary semiconductor dopant toward the mask and mask opening at a first average tilt angle of at least 15° along paths that originate laterally beyond the first transverse mask side such that an electrically significant amount of the first ions passes through the mask opening and enters the channel-zone location and (b) directing second ions of the species of the primary dopant toward the mask and mask opening at a second average tilt angle of at least 15° along paths that originate laterally beyond the second transverse mask side such that the mask, the gate electrode, and any material along the gate electrode substantially block any electrically significant amount of the second ions from entering the channel-zone location, the tilt angles being measured from a perpendicular to a plane extending generally along the body's upper surface; and performing the other of the directing steps.",
    "2. A method as in claim 1 wherein the channel-zone location and the primary dopant are of the same conductivity type.",
    "3. A method as in claim 1 wherein the gate electrode and any material situated on the gate electrode's transverse sides are further away from the first transverse mask side than from the second transverse mask side.",
    "4. A method as in claim 1 wherein the tilt angles are within 10° of each other.",
    "5. A method as in claim 1 wherein the tilt angles are approximately equal.",
    "6. A method as in claim 1 wherein each of the tilt angles is at least 25°.",
    "7. A method as in claim 1 wherein: the paths of the first ions are roughly parallel; and the paths of the second ions are roughly parallel and at a non-zero angle to the paths of the first ions.",
    "8. A method as in claim 1 wherein: the first ions impinge on the mask generally parallel to a first principal impingement axis; the second ions impinge on the mask generally parallel to a second principal impingement axis different from the first principal impingement axis.",
    "9. A method as in claim 8 wherein: each principal axis is at an azimuthal angle, as measured in the plane extending along the body's upper surface, to a channel-length direction for the channel-zone location; the azimuthal angle for the first principal axis differs from 0° by no more than 60°; and the azimuthal angle for the second principal axis differs from 180° by no more than 60°.",
    "10. A method as in claim 9 wherein: the azimuthal angle for the first principal axis differs from 0° by no more than 45°; and the azimuthal angle for the second principal axis differs from 180° by no more than 45°.",
    "11. A method as in claim 9 wherein the principal axes cross each other at an axial angle approximately equal to the sum of the first and second tilt angles.",
    "12. A method as in claim 1 wherein the channel-zone location and the primary dopant are of a first conductivity type, the method further including the step of introducing first semiconductor dopant of a second conductivity type opposite to the first conductivity type through the mask opening, past the gate electrode, and into the semiconductor body to at least partially define a pair of laterally separated source/drain zones using the mask, the gate electrode, and any material along the gate electrode as a dopant-blocking shield.",
    "13. A method as in claim 12 further including, subsequent to substantially removing the mask, the steps of: providing spacer material over the gate electrode's transverse sides; providing a further mask over the semiconductor body, gate electrode, and spacer material such that the further mask has a further mask opening which at least partially overlies the gate electrode and spacer material and which extends laterally beyond the gate electrode and spacer material; and introducing second semiconductor dopant of the second conductivity type through the further mask opening, past the gate electrode and spacer material, and into the semiconductor body to further define the source/drain zones using the further mask, the gate electrode, and the spacer material as a dopant-blocking shield.",
    "14. A method as in claim 13 wherein the semiconductor body and the gate electrode comprise silicon, the method further including the step of forming metal silicide layers along the gate electrode and source/drain zones.",
    "15. A method as in claim 1 wherein the step of directing the second ions includes introducing the second ions into the semiconductor body at a location spaced apart from the channel-zone location.",
    "16. A method as in claim 1 wherein the mask comprises actinic material.",
    "17. A method comprising the steps of: furnishing primary and additional gate electrodes for respective primary and additional like-polarity field-effect transistors above, and vertically separated by gate dielectric material from, respective laterally separated primary and additional intended channel-zone locations in a semiconductor body along its upper surface; providing a mask over the semiconductor body and the gate electrodes such that the mask has at least one mask opening which at least partially overlies the gate electrodes, which defines opposite first and second primary transverse mask sides located laterally beyond the primary gate electrode and any material situated on opposite transverse sides of the primary gate electrode, and which defines opposite first and second additional transverse mask sides located laterally beyond the gate electrode and any material situated on opposite transverse sides of the additional gate electrode; and directing first ions of a species of a primary semiconductor dopant toward the mask and each mask opening at a first average tilt angle of at least 15° along paths that originate laterally beyond the two first transverse mask sides such that an electrically significant amount of the first ions passes through one such mask opening and enters the primary channel-zone location and such that the mask, the additional gate electrode, and any material situated along the additional gate electrode substantially block any electrically significant amount of the first ions from entering the additional channel-zone location, the first tilt angle being measured from a perpendicular to a plane extending generally along the semiconductor body's upper surface.",
    "18. A method as in claim 17 wherein the channel-zone locations and the primary dopant are of the same conductivity type.",
    "19. A method as in claim 17 further including the step of directing second ions of the species of the primary dopant toward the mask and each mask opening at a second average tilt angle of at least 15° along paths that originate laterally beyond the two second transverse mask sides such that the mask, the primary gate electrode, and any material along the primary gate electrode substantially block any electrically significant amount of the second ions from entering the primary channel-zone location and such that an electrically significant amount of the second ions passes through one such mask opening and enters the additional channel-zone location, the second tilt angle being measured from a perpendicular to a plane extending generally along the body's upper surface.",
    "20. A method as in claim 19 wherein: the primary gate electrode and any material situated on the primary gate electrode's transverse sides are further away from the first primary transverse mask side than from the second primary transverse mask side; and the additional gate electrode and any material situated on the additional gate electrode's transverse sides are further away from the second additional transverse mask side than from the first additional transverse mask side.",
    "21. A method as in claim 19 wherein the tilt angles are within 10° of each other.",
    "22. A method as in claim 19 wherein the tilt angles are approximately equal.",
    "23. A method as in claim 19 wherein: the paths of the first ions are roughly parallel; and the paths of the second ions are roughly parallel and at a non-zero angle to the paths of the first ions.",
    "24. A method as in claim 19 wherein: the first ions impinge on the mask generally parallel to a first principal impingement axis; and the second ions impinge on the mask generally parallel to a second principal impingement axis different from the first principal axis.",
    "25. A method as in claim 24 wherein: the channel-zone locations both extend longitudinally in largely a single channel-length direction; each principal axis is at an azimuthal angle, as measured in a plane extending generally along the body's upper surface, to the channel-length direction; the azimuthal angle for the first principal axis differs from 0° by no more than 60°; and the azimuthal angle for the second principal axis differs from 180° by no more than 60°.",
    "26. A method as in claim 17 further including the step of directing second ions of the species of the primary dopant toward the mask and each mask opening at a second average tilt angle of at least 15° along paths that originate laterally beyond the two second transverse mask sides such that an electrically significant amount of the second ions passes through at least one such mask opening and enters each channel-zone location, the second tilt angle being measured from a perpendicular to a plane extending generally along the body's upper surface.",
    "27. A method as in claim 17 further including the step of directing ions of the species of the primary dopant toward the mask and each mask opening at a second average tilt angle of at least 15° along paths that originate laterally beyond the two second transverse mask sides such that the mask, the gate electrodes, and any material along the gate electrodes substantially block any electrically significant amount of the second ions from entering either channel-zone location, the second tilt angle being measured from a perpendicular to a plane extending generally along the body's upper surface.",
    "28. A method as in claim 27 wherein the step of directing the second ions includes introducing the second ions into the semiconductor body at a location spaced apart from both channel-zone locations.",
    "29. A method as in claim 17 wherein the at least one mask opening comprises a pair of laterally separated mask openings, each at least partially overlying a different one of the gate electrodes and extending laterally beyond that gate electrode and any material situated on that gate electrode's transverse sides.",
    "30. A method as in claim 17 wherein the channel-zone locations and the primary dopant are of a first conductivity type, the method further including the step of introducing first semiconductor dopant of a second conductivity type opposite to the first conductivity type through at least one such mask opening, past the gate electrodes' transverse sides, and into the semiconductor body to at least partially define a pair of laterally separate source/drain zones of each transistor using the mask, the gate electrodes, and any material along the gate electrodes as a dopant-blocking shield.",
    "31. A method as in claim 30 further including, subsequent to removing the mask, the steps of: providing spacer material over the gate electrodes' transverse sides; providing a further mask over the semiconductor body and the gate electrodes such that the further mask has at least one further mask opening which at least partially overlies the gate electrodes and spacer material and which extends laterally beyond the gate electrodes and spacer material; and introducing second semiconductor dopant of the second conductivity type through the at least one further mask opening, past the spacer material, and into the semiconductor body to further define the source/drain zones of each transistor using the further mask, the gate electrodes, and the spacer material as a dopant-blocking shield.",
    "32. A method as in claim 17 wherein: the primary gate electrode and any material situated on the primary gate electrode's transverse sides is further away from the first primary transverse mask side than from the second primary transverse mask side; and the additional gate electrode and any material situated on the additional gate electrode's transverse sides is farther away from the second additional transverse mask side than from the first additional transverse mask side.",
    "33. A method as in claim 19 wherein the at least one mask opening comprises a pair of laterally separated mask openings, each at least partially overlying a different one of the gate electrodes and extending laterally beyond that gate electrode and any material situated on that gate electrode's transverse sides.",
    "34. A method as in claim 19 wherein the channel-zone locations and the primary dopant are of a first conductivity type, the method further including the step of introducing first semiconductor dopant of a second conductivity type opposite to the first conductivity type through at least one such mask opening, past the gate electrodes' transverse sides, and into the semiconductor body to at least partially define a pair of laterally separate source/drain zones of each transistor using the mask, the gate electrodes, and any material along the gate electrodes as a dopant-blocking shield.",
    "35. A method as in claim 34 further including, subsequent to removing the mask, the steps of: providing spacer material over the gate electrodes' transverse sides; providing a further mask over the semiconductor body and the gate electrodes such that the further mask has at least one further mask opening which at least partially overlies the gate electrodes and spacer material and which extends laterally beyond the gate electrodes and spacer material; and introducing second semiconductor dopant of the second conductivity type through the at least one further mask opening, past the spacer material, and into the semiconductor body to further define the source/drain zones of each transistor using the further mask, the gate electrodes, and the spacer material as a dopant-blocking shield.",
    "36. A method as in claim 34 wherein the at least one mask opening comprises a pair of laterally separated mask openings, each at least partially overlying a different one of the gate electrodes and extending laterally beyond that gate electrode and any material situated on that gate electrode's transverse sides.",
    "37. A method comprising the steps of: furnishing primary and additional gate electrodes for respective primary and additional like-polarity field-effect transistors above, and vertically separated by gate dielectric material from, respective laterally separated primary and additional intended channel-zone locations in a semiconductor body along its upper surface, the two channel-zone locations having respective substantially parallel channel-length directions; providing a mask over the semiconductor body and the gate electrodes such that the mask has at least one mask opening which at least partially overlies the gate electrodes, which defines opposite first and second primary transverse mask sides located laterally beyond the primary gate electrode and any material situated on opposite transverse sides of the primary gate electrode, and which defines opposite first and second additional transverse mask sides located laterally beyond the gate electrode and any material situated on opposite transverse sides of the additional gate electrode; and directing first ions of a species of a primary semiconductor dopant toward the mask and each mask opening at a first average tilt angle of at least 15° along paths that originate laterally beyond the two first transverse mask sides such that an electrically significant amount of the first ions passes through one such mask opening and enters the primary channel-zone location and such that the mask, the additional gate electrode, and any material situated along the additional gate electrode substantially block any electrically significant amount of the first ions from entering the additional channel-zone location, the first tilt angle being measured from a perpendicular to a plane extending generally along the semiconductor body's upper surface.",
    "38. A method as in claim 37 wherein the channel-zone locations and the primary dopant are of the same conductivity type.",
    "39. A method as in claim 37 further including the step of directing second ions of the species of the primary dopant toward the mask and each mask opening at a second average tilt angle of at least 15° along paths that originate laterally beyond the two second transverse mask sides such that the mask, the primary gate electrode, and any material along the primary gate electrode substantially block any electrically significant amount of the second ions from entering the primary channel-zone location and such that an electrically significant amount of the second ions passes through one such mask opening and enters the additional channel-zone location, the second tilt angle being measured from a perpendicular to a plane extending generally along the body's upper surface.",
    "40. A method as in claim 39 wherein: the primary gate electrode and any material situated on the primary gate electrode's transverse sides are further away from the first primary transverse mask side than from the second primary transverse mask side; and the additional gate electrode and any material situated on the additional gate electrode's transverse sides are further away from the second additional transverse mask side than from the first additional transverse mask side.",
    "41. A method as in claim 39 wherein the tilt angles are within 10° of each other.",
    "42. A method as in claim 37 wherein the at least one mask opening comprises a pair of laterally separated mask openings, each at least partially overlying a different one of the gate electrodes and extending laterally beyond that gate electrode and any material situated on that gate electrode's transverse sides.",
    "43. A method as in claim 38 wherein the channel-zone locations and the primary dopant are of a first conductivity type, the method further including the step of introducing first semiconductor dopant of a second conductivity type opposite to the first conductivity type through at least one such mask opening, past the gate electrodes' transverse sides, and into the semiconductor body to at least partially define a pair of laterally separate source/drain zones of each transistor using the mask, the gate electrodes, and any material along the gate electrodes as a dopant-blocking shield.",
    "44. A method as in claim 43 further including, subsequent to removing the mask, the steps of: providing spacer material over the gate electrodes' transverse sides; providing a further mask over the semiconductor body and the gate electrodes such that the further mask has at least one further mask opening which at least partially overlies the gate electrodes and spacer material and which extends laterally beyond the gate electrodes and spacer material; and introducing second semiconductor dopant of the second conductivity type through the at least one further mask opening, past the spacer material, and into the semiconductor body to further define the source/drain zones of each transistor using the further mask, the gate electrodes, and the spacer material as a dopant-blocking shield."
  ],
  "description_excerpt": "This invention relates to the fabrication and structure of field-effect transistors (“FETs”) of the insulated-gate type. All of the insulated-gate FETs (“IGFETs”) described below are enhancement-mode devices except as otherwise indicated.\n\nAn IGFET is a semiconductor device in which a gate dielectric layer electrically insulates a gate electrode from a channel zone that extends between a source and a drain. The channel zone in an enhancement-mode IGFET is part of a body region that forms respective pn junctions with the source and drain. In an enhancement-mode IGFET, the channel zone consists of all semiconductor body material between the source and drain.\n\nFIG. 1 illustrates a conventional symmetrical n-channel enhancement-mode IGFET 10 provided with a two-part drain for reducing undesired hot-carrier injection. IGFET 10 is created from a monocrystalline silicon semiconductor body having region 12 of lightly doped p-type body material. IGFET 10 has n- type source 14, n- type drain 16, intervening p- type channel zone 18, gate electrode 20, gate dielectric layer 22, and gate sidewall spacers 24 and 26. Drain 16 consists of heavily doped main portion 16 M and more lightly doped extension 16 E. Source 14 similarly consists of heavily doped main portion 14 M and more lightly doped extension 14 E. When IGFET 10 is turned on, electrons travel from source 14 to drain 16 by way of a thin channel induced in channel zone 18 along the upper semiconductor surface.\n\nA pair of depletion regions extend respectively along the drain/body and source/body junctions.",
  "cpc": [
    "H10D 30/0227",
    "H10D 30/0212",
    "H10D 62/307",
    "H10D 84/0167",
    "H10D 84/0177",
    "H10D 84/0179",
    "H10D 84/038",
    "H10P 30/221",
    "H10P 30/222"
  ],
  "ipc": [
    "H01L 21/265",
    "H01L 21/336",
    "H01L 21/8238",
    "H01L 29/10"
  ],
  "assignees": [
    "National Semiconductor Corp"
  ],
  "inventors": [
    "Fu-Cheng Wang",
    "Constantin Bulucea"
  ],
  "filing_date": "2000-03-31",
  "publication_date": "2003-05-20",
  "grant_date": "2003-05-20",
  "priority_date": "2000-03-31",
  "application_number": "US-54073400-A",
  "family_id": "24156706",
  "cited_by_count": 142,
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}