Process for high density flash EPROM cell
First Claim
1. A method of forming a floating surrounding-gate memory cell, for an electrically programmable read-only memory (EPROM) or flash-memory, comprising the steps of:
- forming a well in a silicon substrate by implantation of a first conductivity type dopant;
forming silicon mesas from said well, by anisotropically etching portions of said device-well, wherein said mesas remain at the unetched portions of said device-well;
forming source regions in said device-well in the regions between said silicon mesas, by implanting with a second and opposite conductivity type dopant to said first conductivity type dopant, and simultaneously forming drain regions in the top of said silicon mesas by said implanting with a second and opposite conductivity type dopant;
forming a first oxide layer over horizontal and vertical surfaces of said silicon mesas and over said source regions;
anisotropically etching said first oxide layer to remove said first oxide layer from all said horizontal surfaces;
forming a second oxide layer over said silicon mesas, said first oxide layer and said source regions, whereby a gate oxide is formed along said vertical surfaces of said silicon mesas, and a tunnel oxide that is thinner than said gate oxide is formed over said source regions;
forming a first conductive layer over said gate oxide, thereby creating said surrounding-gate for said floating memory cell;
forming an interpoly dielectric layer over the vertical surfaces of said first conductive layer, and horizontally over said source regions; and
forming a second conductive layer over said interpoly dielectric layer, which acts as a control gate and word line for said memory cell.
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Abstract
A method and structure for manufacturing a high-density EPROM or flash memory cell is described. A structure having silicon islands is formed from a device-well that has been implanted with a first conductivity-imparting dopant, over a silicon substrate. A first dielectric layer surrounds the vertical surfaces of the silicon islands, whereby the first dielectric layer is a gate oxide. A first conductive layer is formed over vertical surfaces of the first dielectric layer, and acts as the floating surrounding-gate for the memory cell. A source region is formed in the device-well by implanting with a second and opposite conductivity-imparting dopant to the first conductivity-imparting dopant, and surrounds the base of the silicon islands. A drain region is in the top of the silicon islands, formed by implanting with a second and opposite conductivity-imparting dopant to the first conductivity-imparting dopant. A thin dielectric layer surrounds the silicon islands, over the source region and under the first conductive layer, and acts as a tunnel oxide for the memory cell. A second dielectric layer is formed over vertical surfaces of the first conductive layer, and horizontally over the source region, and is an interpoly dielectric. A second conductive layer is formed over vertical surfaces of the second dielectric layer, and is the control gate for the memory cell.
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Citations
8 Claims
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1. A method of forming a floating surrounding-gate memory cell, for an electrically programmable read-only memory (EPROM) or flash-memory, comprising the steps of:
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forming a well in a silicon substrate by implantation of a first conductivity type dopant; forming silicon mesas from said well, by anisotropically etching portions of said device-well, wherein said mesas remain at the unetched portions of said device-well; forming source regions in said device-well in the regions between said silicon mesas, by implanting with a second and opposite conductivity type dopant to said first conductivity type dopant, and simultaneously forming drain regions in the top of said silicon mesas by said implanting with a second and opposite conductivity type dopant; forming a first oxide layer over horizontal and vertical surfaces of said silicon mesas and over said source regions; anisotropically etching said first oxide layer to remove said first oxide layer from all said horizontal surfaces; forming a second oxide layer over said silicon mesas, said first oxide layer and said source regions, whereby a gate oxide is formed along said vertical surfaces of said silicon mesas, and a tunnel oxide that is thinner than said gate oxide is formed over said source regions; forming a first conductive layer over said gate oxide, thereby creating said surrounding-gate for said floating memory cell; forming an interpoly dielectric layer over the vertical surfaces of said first conductive layer, and horizontally over said source regions; and forming a second conductive layer over said interpoly dielectric layer, which acts as a control gate and word line for said memory cell. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification