Multiple spacer formation/removal technique for forming a graded

Details Multiple spacer formation/removal technique for forming a graded Multiple spacer formation/removal technique for forming a graded

1996-12-06

1998-06-16

Chaudhari, Chandra

Fishing, trapping, and vermin destroying

437 30, 437934, H01L 21266

Patent

active

057669694

ABSTRACT:
A transistor and a transistor fabrication method are presented where a sequence of spacers are formed and partially removed upon sidewall surfaces of the gate conductor to produce a graded junction having a relatively smooth doping profile. The spacers include removable and non-removable structures formed on the sidewall surfaces. The adjacent structures have dissimilar etch characteristics compared to each other and compared to the gate conductor. A first dopant (MDD dopant) and a second dopant (source/drain dopant) are implanted into the semiconductor substrate after the respective formation of the removable structure and the non-removable structure. A third dopant (LDD dopant) is implanted into the semiconductor substrate after the removable layer is removed from between the gate conductor and the non-removable structure (spacer). As a result a graded junction is created having higher concentration regions formed outside of lightly concentration regions, relative to the channel area. Such a doping profile provides superior protection against the hot-carrier effect compared to the traditional LDD structure. The smoother the doping profile, the more gradual the voltage drop across the channel/drain junction. A more gradual voltage drop gives rise to a smaller electric field and reduces the hot-carrier effect. Furthermore, the MDD and source/drain implants are performed first, prior to the LDD implant. This allows high-temperature thermal anneals to be performed first, followed by lower temperature anneals second.

REFERENCES:
patent: 4843023 (1989-06-01), Chiu et al.
patent: 5153145 (1992-10-01), Lee et al.
patent: 5168072 (1992-12-01), Moslehi
patent: 5405791 (1995-04-01), Ahmad et al.

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