Semiconductor device manufacturing: process – Chemical etching – Combined with coating step
Reexamination Certificate
1999-03-11
2001-01-09
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Chemical etching
Combined with coating step
C438S700000
Reexamination Certificate
active
06171969
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the manufacture of integrated circuits, and more specifically, to the implantation of dopants into mesas and other elevated structures on semiconductor wafers.
BACKGROUND OF THE INVENTION
Semiconductors are widely used in integrated circuits for electronic applications, including radios, computers and televisions. Such integrated circuits typically use multiple transistors fabricated in single crystal silicon. A feature of semiconductors that make them so useful for electronic devices is that their conduction properties may be changed by introducing small quantities of dopant atoms.
Ion implantation is a method of introducing dopants into semiconductor surfaces. Ion implantation introduces impurities into a semiconductor wafer by accelerating ions to a high velocity and directing them towards the wafer surface. The dopant atoms enter the crystal lattice of the wafer, collide with surface substrate atoms and gradually lose energy, finally coming to rest at some depth within the lattice. During ion implantation, ions travel in a relatively straight path initially, then travel in a zigzag path during which nuclear collisions absorb energy until they stop moving and settle into the solid at a particular range. Each ion is subject to a slightly different set of conditions and thus has a different range.
When devices such as, for example, transistors, thyristors, diodes, etc., are formed in a semiconductor surface, active areas or mesas are created. These mesas may be doped in a subsequent step by ion implantation.
SUMMARY OF THE INVENTION
A problem in the prior art is non-uniformity of ion implantation on mesas in a semiconductor surface that results from implanting ions after the mesas have been formed. Lateral ion straggling causes a non-uniformity of dopant concentration because fewer ions are implanted at the edge of the mesas. Lateral ion straggling results in ions leaving the edge of the mesa and thus exiting the elevated semiconductor surface, with fewer ions being implanted at the edge of the mesas. A uniform, controllable, and reproducible method of introducing a dopant to the surface of a mesa is needed in the art. Another problem in the prior art is that recessed areas are also doped during the ion implantation process, which may not be desired.
These problems of the prior art are overcome by the present invention. The present invention is a method for manufacturing a uniformly-doped mesa on a semiconductor surface, including the steps of providing a semiconductor wafer, doping the surface of the semiconductor wafer and forming mesas in the semiconductor surface.
The present invention of doping the semiconductor surface before forming the mesas offers definite advantages over conventional processes. A mesa structure is provided that contains improved uniform dopant distribution, and where the trenches of the semiconductor wafer are not doped, eliminating the problems of the prior art.
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Brady III W. James
Garner Jacqueline J.
Nelms David
Nhu David
Telecky , Jr. Frederick J.
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