Method for making improved polysilicon FET gate electrodes having composite sidewall spacers using a trapezoidal-shaped insulating layer for more reliable integrated circuits
First Claim
1. A method for making FET gate electrodes having composite sidewall spacers using a trapezoidal-shaped insulating layer comprising the steps of:
- providing a semiconductor substrate having device areas surrounded and electrically isolated by field oxide areas;
forming a gate oxide on said device areas;
depositing a polysilicon layer on said device areas and elsewhere on said substrate, said polysilicon layer being conductively doped;
patterning said polysilicon layer to form said FET gate electrodes on said device areas;
forming lightly doped source/drain areas adjacent to said FET gate electrodes;
depositing a first insulating layer on said FET gate electrodes, said first insulating layer having a trapezoidal shape over said FET gate electrodes such that only the top edges of said FET gate electrodes are free of said first insulating layer;
depositing a conformal second insulating layer on said first insulating layer;
anisotropically plasma etching said second insulating layer to said first insulating layer to form said sidewall spacers on sidewalls of said FET gate electrodes, said first insulating layer acting as an etch endpoint detect;
removing said first insulating layer remaining on said lightly doped source/drain areas using a wet etch, while said second insulating layer protects said first insulating layer at top edges of said FET gate electrodes;
forming source/drain contact areas adjacent to said sidewalls of said FET gate electrodes in said device areas;
depositing a blanket third insulating layer on said substrate and planarizing;
etching contact openings in said third insulating layer to said source/drain contact areas, while said second insulating layer protects said first insulating layer at top edges of said FET gate electrodes when etching said contact openings that extend over said FET gate electrodes.
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Abstract
A method for making improved polysilicon FET gate electrodes having composite sidewall spacers is achieved. After forming the polysilicon gate electrodes on the substrate, a SiO2 stress-release layer is deposited having a trapezoidal shape. A Si3 N4 layer is deposited and plasma etched back using the SiO2 layer as an etch-endpoint-detect layer to form composite sidewall spacers that include portions of the trapezoidal-shaped oxide layer. The SiO2 layer protects the source/drain areas from plasma etch damage that could cause high leakage currents. The Si3 N4 also extends over the SiO2 layer at the upper edges of the polysilicon gate electrodes. This prevents erosion of the SiO2 along the gate electrodes when the remaining oxide is removed from the source/drain areas using hydrofluoric acid wet etching. When an insulating layer is deposited over the FETs, and self-aligned contact openings are etched to the source/drain areas and extending over the gate electrodes, the Si3 N4 extending over the portion of the trapezoidal-shaped SiO2 layer that forms part of the composite sidewall spacer protects the SiO2 from etching. This results in more reliable contacts without degrading the FET performance.
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Citations
20 Claims
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1. A method for making FET gate electrodes having composite sidewall spacers using a trapezoidal-shaped insulating layer comprising the steps of:
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providing a semiconductor substrate having device areas surrounded and electrically isolated by field oxide areas; forming a gate oxide on said device areas; depositing a polysilicon layer on said device areas and elsewhere on said substrate, said polysilicon layer being conductively doped; patterning said polysilicon layer to form said FET gate electrodes on said device areas; forming lightly doped source/drain areas adjacent to said FET gate electrodes; depositing a first insulating layer on said FET gate electrodes, said first insulating layer having a trapezoidal shape over said FET gate electrodes such that only the top edges of said FET gate electrodes are free of said first insulating layer; depositing a conformal second insulating layer on said first insulating layer; anisotropically plasma etching said second insulating layer to said first insulating layer to form said sidewall spacers on sidewalls of said FET gate electrodes, said first insulating layer acting as an etch endpoint detect; removing said first insulating layer remaining on said lightly doped source/drain areas using a wet etch, while said second insulating layer protects said first insulating layer at top edges of said FET gate electrodes; forming source/drain contact areas adjacent to said sidewalls of said FET gate electrodes in said device areas; depositing a blanket third insulating layer on said substrate and planarizing; etching contact openings in said third insulating layer to said source/drain contact areas, while said second insulating layer protects said first insulating layer at top edges of said FET gate electrodes when etching said contact openings that extend over said FET gate electrodes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for making FET gate electrodes having composite sidewall spacers using a trapezoidal-shaped insulating layer comprising the steps of:
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providing a semiconductor substrate having device areas surrounded and electrically isolated by field oxide areas; forming a gate oxide on said device areas; depositing a polysilicon layer on said device areas and elsewhere on said substrate, said polysilicon layer being conductively doped; patterning said polysilicon layer to form said FET gate electrodes on said device areas; forming lightly doped source/drain areas adjacent to said FET gate electrodes; depositing a first insulating layer composed of silicon oxide on said FET gate electrodes, said first insulating layer having a trapezoidal shape over said FET gate electrodes such that only the top edges of said FET gate electrodes are free of said first insulating layer; depositing a conformal second insulating layer composed of silicon nitride on said first insulating layer; anisotropically plasma etching said second insulating layer to said first insulating layer to form said sidewall spacers on sidewalls of said FET gate electrodes, said first insulating layer acting as an etch endpoint detect; removing said first insulating layer remaining on said lightly doped source/drain areas using a hydrofluoric acid wet etch, while said second insulating layer protects said first insulating layer at top edges of said FET gate electrodes; forming source/drain contact areas adjacent to said sidewalls of said FET gate electrodes in said device areas; depositing a blanket third insulating layer on said substrate and planarizing; etching contact openings in said third insulating layer to said source/drain contact areas, while said second insulating layer protects said first insulating layer at top edges of said FET gate electrodes when etching said contact openings that extend over said FET gate electrodes. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification