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. 10, 1994
Filed:
May. 27, 1993
Applicant:
Inventor:
Kakutaro Suda, Itami, JP;
Assignee:
Mitsubishi Denki Kabushiki Kaisha, Tokyo, JP;
Primary Examiner:
Assistant Examiner:
Int. Cl.
CPC ...
H01L / ;
U.S. Cl.
CPC ...
437 31 ; 437 69 ; 437 56 ; 437 34 ; 437 67 ; 437924 ;
Abstract
A p.sup.- semiconductor substrate has a surface which is high in a memory cell region and low in a peripheral circuit region. An n.sup.+ buried semiconductor layer of uniform thickness is formed on the substrate. An n.sup.- epitaxial layer formed on the buried semiconductor layer is thin in the memory cell region and thick in the peripheral circuit region, so that the surface of the epitaxial layer can be flat. A concave or convex step is formed on the surface of the epitaxial layer in a boundary portion between the memory cell region and the peripheral circuit region in order to use it as an alignment mark in a later processing step.