Trenched Schottky rectifiers

• US 6,441,454 B2
• Filed: 02/01/2001
• Issued: 08/27/2002
• Est. Priority Date: 02/02/2000
• Status: Expired due to Term

• Current Assignee: Callahan Cellular LLC (Intellectual Ventures LLC)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Hueting, Raymond J. E., Hijzen, Erwin A.
• Primary Examiner(s): Lee, Eddie
• Assistant Examiner(s): RICHARDS, NORMAN DREW
• Application Number:
  US09/773,412
• Publication Number:
  US 20010010385A1
• Time in Patent Office: 572 Days
• Field of Search: 257/471, 257/475, 257/483, 257/484, 257/488, 257/492, 257/493, 257/339, 257/355
• US Class Current: 257/483
• CPC Class Codes: H01L 29/407 Recessed field plates, e.g. trench field plates, buried field plates
• CPC Class Codes: H01L 29/872 Schottky diodes
• CPC Class Codes: H01L 29/8725 of the trench MOS barrier type [TMBS]

Abstract

Inner trenches (11) of a trenched Schottky rectifier (1a; 1b; 1c; 1d) bound a plurality of rectifier areas (43a) where the Schottky electrode (3) forms a Schottky barrier 43 with a drift region (4). A perimeter trench (18) extends around the outer perimeter of the plurality of rectifier areas (43a). These trenches (11, 18) accommodate respective inner field-electrodes (31) and a perimeter field-electrode (38) that are connected to the Schottky electrode (3). The inner field-electrodes (11) are capacitively coupled to the drift region (4) via dielectric material (21) that lines the inner trenches (11). The perimeter field-electrode (38) is capacitively coupled across dielectric material (28) on the inside wall (18a) of the perimeter trench 18, without acting on any outside wall (18b). Furthermore, the inner and perimeter trenches (11, 18) are closely spaced and the intermediate areas (4a, 4b) of the drift region (4) are lowly doped. The spacing is so close and the doping is so low that the depletion layer (40) formed in the drift region (4), from the Schottky barrier (43) and from the field-relief regions (31,21; 38,28) in the blocking state of the rectifier, may deplete the whole of the intermediate areas (4a, 4b) between the trenches (11, 18) at a blocking voltage just below the breakdown voltage. This arrangement reduces the risk of premature breakdown that can occur at high field points in the depletion layer (40), especially at the perimeter of the array of rectifier areas (43a).

Claims

1. A Schottky rectifier comprising a semiconductor body having a body portion of one conductivity type between first and second main electrodes, of which the first main electrode forms a Schottky barrier with the body portion at a plurality of rectifier areas of a first surface of the body portion, and a pattern of trenches extending into the body portion from the first surface, the pattern comprising inner trenches that bound each rectifier area and a perimeter trench that has an inside wall extending around the outer perimeter of the plurality of rectifier areas, the trenches accommodating a field-electrode that is connected to the first main electrode, the field-electrode being capacitively coupled to the body portion via dielectric material that lines the trenches so as to provide field-relief regions in the body portion, a depletion layer being formed in the body region from the Schottky barrier and from the field-relief regions in a blocking state of the rectifier, characterised in that the field-electrode in the perimeter trench is present on dielectric material on said inside wall of the perimeter trench and is capacitively coupled across said inside wall without acting on any outside wall, and in that the inner and perimeter trenches are sufficiently closely spaced and the intermediate areas of the body portion are sufficiently lowly doped that the depletion layer formed in the body portion in the blocking state of the rectifier depletes the whole of the intermediate areas of the body portion between the trenches at a voltage less than the breakdown voltage.

2. A rectifier as claimed in claim 1, further characterised in that the perimeter trench extends deeper in the body than the inner trenches.

3. A rectifier as claimed in claim 2, further characterised in that the body portion comprises a drift region present on a higher conductivity substrate of the same one conductivity type, and the perimeter trench extends through the thickness of the drift region to the substrate.

4. A rectifier as claimed in claim 1, further characterised in that the perimeter trench is wider than the inner trenches.

5. A rectifier as claimed in claim 4, further characterised in that the perimeter trench extends to the perimeter of the semiconductor body and so provides no outside wall.

6. A rectifier as claimed in claim 1, further characterised in that the dielectric material that lines at least a lower part of the perimeter trench is thicker than the dielectric material that lines at least an upper part of the inner trenches.

7. A rectifier as claimed in claim 1, further characterised in that the body portion comprises a drift region present on a higher conductivity substrate of the same one conductivity type, and the drift region has distinct surface-adjacent and substrate-adjacent portions which are of different doping concentrations, the surface-adjacent portion having a lower doping concentration than the substrate-adjacent portion.

8. A rectifier as claimed in claim 1, further characterised in that the body portion comprises a drift region present on a higher conductivity substrate of the same one conductivity type, and the substrate-adjacent portion of the drift region has a graded doping concentration that increases with distance to the substrate.

9. A rectifier as claimed in claim 7, further characterised in that the dielectric material that lines the inner trenches is of increased thickness in the substrate-adjacent portion of the drift region as compared with its thickness in the surface-adjacent portion.

10. A rectifier as claimed in claim 9, further characterised in that the dielectric material that lines at least a lower part of the perimeter trench is of the same composition and thickness as the composition and increased thickness of the dielectric material of the inner trenches in the substrate-adjacent portion of the drift region.

11. A rectifier as claimed in claim 1, further characterised in that the body portion of the one conductivity type extends to the surface between the outermost inner trench and the perimeter trench.

12. A rectifier as claimed in claim 1, further characterised in that a breakdown shielding region of the opposite conductivity type is present between the outermost inner trench and the perimeter trench and forms a p—

n junction with the body portion of the one conductivity type.

13. A method of manufacturing a rectifier as claimed in claim 4, wherein the wider, deeper perimeter trench and the inner trenches are etched into the semiconductor body using the same process steps and via respective windows in a masking pattern on the surface of the body, and wherein the windows for the inner trenches are so narrow as to restrict the etch rate for the array trenches as compared with a wider window for the perimeter trench.