Vertical trench-gated power MOSFET having stripe geometry and high cell density

• US 6,204,533 B1
• Filed: 06/02/1998
• Issued: 03/20/2001
• Est. Priority Date: 06/02/1995
• Status: Expired due to Term

• Current Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Original Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Inventors: Grabowski, Wayne B., Williams, Richard K.
• Primary Examiner(s): Prenty, Mark V.
• Application Number:
  US09/089,250
• Time in Patent Office: 1,022 Days
• Field of Search: 257/341, 257/342, 257/331
• US Class Current: 257/341
• CPC Class Codes: H01L 27/0255 using diodes as protective elements
• CPC Class Codes: H01L 27/0727 in combination with diodes, or capacitors or resistors
• CPC Class Codes: H01L 29/0696 of cellular field-effect devices, e.g. multicellular DMOS transistors or IGBTs
• CPC Class Codes: H01L 29/1095 Body region, i.e. base region, of DMOS transistors or IGBTs cell layout H01L29/0696
• CPC Class Codes: H01L 29/7808 the other device being a breakdown diode, e.g. Zener diode
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236
• CPC Class Codes: H01L 29/7827 Vertical transistors H01L29/7802, H01L29/78642 take precedence

Abstract

A vertical trench-gated power MOSFET includes MOSFET cells in the shape of longitudinal stripes. The body diffusion of each cell contains a relatively heavily-doped region which extends parallel to the length of the cell and contacts an overlying metal source/body contact layer at specific locations. In one embodiment, the contact is made at an end of the cell. In another embodiment, the contact is made at intervals along the length of the cell. In addition, the power MOSFET contains diode cells placed at intervals in the array of cells. The diode cells contain diodes connected in parallel with the MOSFET cells and protect the gate oxide layer lining the trenches from damage due to large electric fields and hot carrier injection. By restricting the areas where the body contact is made and using the diode cells, the width of the MOSFET cells can be reduced substantially, thereby reducing the on-resistance of the power MOSFET.

Claims

1. A power MOSFET formed in a semiconductor chip, said MOSFET comprising:

at least one MOSFET cell, said cell being formed in the shape of a longitudinal stripe having a length and a width, said stripe being located between opposing gate sections and having a top surface coincident with a surface of said chip, each of said gate sections being formed in a trench, said MOSFET cell comprising;

a source region of a first conductivity type located adjacent a portion of said top surface;

a body region of a second conductivity type located beneath said source region, said body region containing a channel region adjacent a wall of said trench;

a drain region of said first conductivity type adjoining said body region; and

a heavily-doped region within said body region, said heavily-doped region being of said second conductivity type and having a dopant concentration greater than a dopant concentration of a remainder of said body region, said heavily-doped region extending along said length of said cell and including at least one contact portion which extends to said surface of said cell.

2. The power MOSFET of claim 1 wherein said heavily-doped region has a dopant concentration of from 5×

10¹⁸ to 8×

10¹⁹ cm<sup>−

3</sup>.

3. The power MOSFET of claim 2 wherein said body region has a dopant concentration of from 8×

10¹⁵ to 7×

10¹⁷ cm<sup>−

3</sup>.

4. The power MOSFET of claim 1 wherein said cell has a length which is at least ten times a width of said cell.

5. The power MOSFET of claim 1 comprising a plurality of rows of said stripe cells, the number of said rows being less than ten.

6. The power MOSFET of claim 1 wherein said contact portion is located at an end of said cell.

7. The power MOSFET of claim 1 comprising a plurality of said contact portions located at intervals along a length of said cell.

8. The power MOSFET of claim 1 wherein said contact portion comprises a band extending along a length of said cell, said band being located approximately equidistant between said gate sections.