Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – Ion implantation of dopant into semiconductor region
Reexamination Certificate
1998-12-02
2001-02-06
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
Ion implantation of dopant into semiconductor region
C438S162000, C438S181000
Reexamination Certificate
active
06184112
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor processing technology, and in particular, the present invention relates to a method of forming a MOSFET transistor with a shallow abrupt retrograde dopant profile.
BACKGROUND OF THE INVENTION
“A retrograde dopant profile” refers to a dopant profile which has a lower dopant concentration at a surface of an object than in the body of the object. Retrograde dopant profiles are known to be useful in the channel region of a metal-oxide-silicon field effect transistor (“MOSFET”) to increase mobility and drive current in the channel region. However, there is an increasing need, as feature sizes of circuits become continuously smaller, to increase mobility and drive current in the channel region, particularly in short channel devices.
Since the advent of semiconductor devices, the minimum feature size has continuously decreased. In order to further decrease the minimum feature size, which is already well into the sub-micron realm, it is important to not only reduce the horizontal dimensions of the devices, but to also reduce the vertical dimensions such as, for example, the retrograde dopant profiles described above.
Conventionally, retrograde dopant profiles may be formed by implanting dopant ions into a semiconductor wafer so that the peak concentration is below the surface of the wafer. However, there is a need to form retrograde dopant profiles which are shallower and more abrupt in order to accommodate the continuously decreasing depths.
Accordingly, there is a need for a method of forming a more abrupt and shallow retrograde dopant profile than conventionally known.
SUMMARY OF THE INVENTION
In accordance with the present invention, an amorphous layer is formed in a crystalline substrate (e.g., in the channel region of a MOSFET) by, for example, implanting ions of an inert specie such as germanium. The amorphous layer is formed a certain distance below the surface, thus leaving a crystalline layer between the amorphous layer and the surface of the crystalline substrate. A dopant is implanted into the crystalline substrate in the channel region before or after the amorphous layer is formed to form a doped region. The doped region overlaps part or all of the amorphous layer. Next, the amorphous layer is recrystallized.
The recrystallization of the amorphous layer activates many ions of part of the doped region overlapping with the amorphous layer. In contrast, the recrystallization annealling does not cause significant activation of ions in the regions that were not amorphized. Therefore, an abrupt retrograde dopant profile can be created at or near the boundary of the recrystallized layer and the crystalline layer in the channel region of the MOSFET.
The shallow abrupt retrograde dopant profile formed in the channel region of a MOSFET controls short channel effects and increases mobility in the channel region.
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Krishnan Srinath
Maszara Witold P.
Pramanick Shekhar
Advanced Micro Devices , Inc.
Hullinger Robert A.
Kwok Edward C.
Skjerven Morrill & MacPherson LLP
Smith Matthew
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