Step-shaped floating poly-si gate to improve gate coupling ratio for flash memory application
First Claim
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1. A stacked-gate flash memory cell having a floating Poly-Si gate with multiply connected surfaces of different shapes comprising:
- providing a semiconductor substrate;
a floating Poly-Si gate with multiply connected surfaces of different shapes;
an inter-poly dielectric layer over said floating Poly-Si gate; and
a Poly-Si control gate over said inter-poly dielectric layer.
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Abstract
A stacked-gate flash memory cell is provided having step-shaped poly-gates with increased overlap area between them in order to increase the coupling ratio and hence the program speed of the cell. The floating gate is first formed with a step and the intergate dielectric is conformally shaped thereon followed by the forming of the control gate thereon. The increase in the overlap area can be achieved by forming gates with multiply connected surfaces of different shapes.
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Citations
20 Claims
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1. A stacked-gate flash memory cell having a floating Poly-Si gate with multiply connected surfaces of different shapes comprising:
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providing a semiconductor substrate;
a floating Poly-Si gate with multiply connected surfaces of different shapes;
an inter-poly dielectric layer over said floating Poly-Si gate; and
a Poly-Si control gate over said inter-poly dielectric layer. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of forming a stacked-gate flash memory having a floating Poly-Si gate with multiply connected surfaces of different shapes comprising the steps of:
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providing a semiconductor substrate;
forming a gate-oxide layer over said substrate;
forming a first polysilicon layer over said gate-oxide layer;
forming multiply connected surfaces of different shapes in said first polysilicon layer;
forming a first polysilicon (Poly-Si) floating gate having said surfaces of different shapes;
forming an inter-poly oxide layer over said floating Poly-Si gate having said surface of different shapes; and
forming a Poly-Si control gate over said floating Poly-Si gate. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A method of forming a stacked-gate flash memory cell having a step-shaped floating Poly-Si gate comprising the steps of:
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providing a semiconductor substrate;
forming a gate-oxide layer over said substrate;
forming a first polysilicon layer over said gate-oxide layer;
forming a mask layer over said pad-oxide layer;
patterning and forming an opening in said mask layer to define a floating gate region in said substrate;
forming spacers in said opening and to expose said first polysilicon layer in said opening;
performing a partial etch of said first polysilicon layer exposed in said opening to form a step-shaped surface on said first polysilicon layer;
removing said spacers and said mask layer;
forming a step-shaped inter-poly dielectric layer over said substrate including said floating Poly-Si gate with said step-shaped surface;
forming a second polysilicon layer over said step-shaped inter-poly dielectric layer;
removing said second polysilicon layer and underlying said inter-poly oxide layer from said substrate, excluding from regions over floating Poly-Si gate, thus forming a Poly-Si control gate having step-shaped surface corresponding to said floating Poly-Si gate with step-shaped surface; and
performing ion implantation to form source and drain of said stacked-gate flash memory cell. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification