US 9,812,550 B2
Semiconductor structure with multiple transistors having various threshold voltages
Dalong Zhao, San Jose, CA (US); Teymur Bakhishev, San Jose, CA (US); Lance Scudder, Sunnyvale, CA (US); Paul E. Gregory, Palo Alto, CA (US); Michael Duane, San Carlos, CA (US); U. C. Sridharan, San Jose, CA (US); Pushkar Ranade, Los Gatos, CA (US); Lucian Shifren, San Jose, CA (US); and Thomas Hoffmann, Los Gatos, CA (US)
Assigned to Mie Fujitsu Semiconductor Limited, Kuwana (JP)
Filed by Mie Fujitsu Semiconductor Limited, Kuwana (JP)
Filed on Jan. 30, 2017, as Appl. No. 15/419,315.
Application 15/047,052 is a division of application No. 13/926,555, filed on Jun. 25, 2013, granted, now 9,299,698, issued on Mar. 29, 2016.
Application 15/419,315 is a continuation of application No. 15/047,052, filed on Feb. 18, 2016.
Claims priority of provisional application 61/665,113, filed on Jun. 27, 2012.
Prior Publication US 2017/0141209 A1, May 18, 2017
Int. Cl. H01L 29/66 (2006.01); H01L 21/265 (2006.01); H01L 21/283 (2006.01); H01L 21/8234 (2006.01); H01L 27/088 (2006.01)
CPC H01L 29/66537 (2013.01) [H01L 21/265 (2013.01); H01L 21/283 (2013.01); H01L 21/823412 (2013.01); H01L 27/088 (2013.01)] 1 Claim
OG exemplary drawing
 
1. A method of fabricating a semiconductor structure, comprising:
implanting in a substrate a first antipunchthrough region with a first doping concentration;
implanting in the substrate a second antipunchthrough region with a second doping concentration;
implanting in the substrate a screening region with a third doping concentration;
forming a substantially undoped channel on the substrate;
forming a gate on the substrate;
implanting in the substrate a source and a drain;
wherein the screening region is located to be below a surface of the substrate at a distance of at least less than 1.5 times a length of the gate and above a bottom of the source and drain to which the screening region abuts;
wherein the first antipunchthrough region underlies the screening region and the first doping concentration is less than the third doping concentration;
wherein the second antipunchthrough region underlies the first antipunchthrough region and the second doping concentration is less than the third doping concentration.