The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 02, 1995
Filed:
Oct. 13, 1993
Kuo-Hua Lee, Wescosville, PA (US);
Chen-Hua D Yu, Allentown, PA (US);
AT&T Corp., Murray Hill, NJ (US);
Abstract
A method for forming a twin tub semiconductor integrated circuit is disclosed. A portion of a semiconductor substrate is masked by oxide, nitride and photoresist. P-type dopant is directed towards the other portion of the substrate. Subsequently, the photoresist is removed and a protective oxide is grown over the p-tub, thereby driving the dopant into the substrate. Next, an n-type ion implantation is performed to create the n-tub. The n-type ions are directed at the substrate at an angle which is away from normal incidence. The angular direction of the n-type dopants permits the use of smaller screen oxides over the n-tub and smaller protective oxides over the already-formed p-tub. When all of the protective oxides have been removed, the inventive technique provides a twin tub substrate having a comparatively smooth upper surface.