Plasma etching of ion-implanted polysilicon
Ion implantation is increasingly used to dope polysilicon gates to obtain lower resistivities and also to control the cumulative time-temperature cycling of VLSI wafers. Dry etching of polysilicon doped with phosphorus by ion implantation was studied using a parallel-plate etcher and two different etch chemistries sulfur haxafluoride-O{sub 2}-argon and SF6-CCl2F2-Ar. These two etch procedures were previously found to result in excellent etching of polysilicon which was doped with phosphorus by solid-source diffusion. Large differences in the cross-sectional profiles of ion-implanted polysilicon were found while using the two chemistries. SF6-dichlorodifluoromethane-Ar chemistry caused sharp notch-like undercuts, while the SF6-O2-Ar chemistry exhibited linewidth loss without any notching. Examples of the cross sections of ion-implanted polysilicon are presented along with a discussion of the possible mechanisms that cause the different cross-sectional profiles in the two etch chemistries. The notching is explained in terms of the variation in the dopant concentration and in the structure of ion-implanted polysilicon at different depths. The absence of notching in the cross section of ion-implanted polysilicon etched in the SF6-O2-Ar chemistry is explained by proposing that the interaction of oxygen in the SF6-O2-Ar chemistry with the etched surface makes the chemistry less sensitive to the dopant concentration in the etched material. Results of a simple experiment which support the proposed explanation are presented.
- Research Organization:
- Massachusetts Inst. of Tech., Lexington, MA (USA). Lincoln Lab.
- OSTI ID:
- 7167552
- Report Number(s):
- AD-A-214152/1/XAB; JA--6165
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360605* -- Materials-- Radiation Effects
42 ENGINEERING
426000 -- Engineering-- Components
Electron Devices & Circuits-- (1990-)
ALKANES
ARGON
CHARGED PARTICLES
CHLORIDES
CHLORINE COMPOUNDS
CRYSTALS
DIFFUSION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRONIC CIRCUITS
ELEMENTS
ETCHING
FLUIDS
FLUORIDES
FLUORINE COMPOUNDS
GASES
GATING CIRCUITS
HALIDES
HALOGEN COMPOUNDS
HYDROCARBONS
INTEGRATED CIRCUITS
ION IMPLANTATION
IONS
METHANE
MICROELECTRONIC CIRCUITS
NONMETALS
ORGANIC COMPOUNDS
OXYGEN
PHOSPHORUS IONS
PHYSICAL PROPERTIES
POLYCRYSTALS
RARE GASES
SEMIMETALS
SILICON
SOLIDS
SULFUR COMPOUNDS
SULFUR FLUORIDES
SURFACE FINISHING
VARIATIONS