Method of forming dual spacer for self aligned contact integration
First Claim
1. A method of forming dual sidewall spacers for a semiconductor device, wherein some transistors have a shorter lightly doped drain, comprising the steps of:
- a) forming a plurality of transistor gates on a semiconductor substrate, wherein each of the gates comprises a silicon nitride insulator above a polysilicon gate electrode,b) ion implanting said semiconductor substrate using said gates as a mask to form lightly doped drain regions,c) forming silicon nitride spacers on the sidewalls of each gate,d) forming heavily doped first drain and first source regions in a non-memory region in said substrate using the silicon nitride spacer as a mask,e) forming silicon oxide spacers over said silicon nitride spacers,f) forming heavily doped second drain and second source regions in a memory region in said substrate using said silicon oxide spacers as a mask,g) depositing an interpoly oxide layer over said substrate,h) forming opening in said interpoly oxide layer in said non-memory region, exposing gate sidewall spacers,i) removing said silicon oxide spacers from within said openingj) forming a self aligned contact in said opening.
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Abstract
In this invention two side wall spacers are applied to the vertical structure of a gate. The first spacer made of Si3 N4 provides for SAC (self aligned contact) definition and the second spacer made of SiO2 is used for the definition of the LDD (lightly doped drain). The second spacer is the outer spacer and is anisotropically etched when the IPO (inter-poly-oxide) is etched to open a SAC contact area for second level polysilicon deposition. This allows a spacer width for the desired length of the LDD while providing a wider width for SAC contact. The SAC contact is not limited by the LDD spacer and the LDD spacer can be optimized without considering the SAC requirements. This invention is easily applied to SRAMS and DRAMS without extra masking.
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Citations
7 Claims
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1. A method of forming dual sidewall spacers for a semiconductor device, wherein some transistors have a shorter lightly doped drain, comprising the steps of:
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a) forming a plurality of transistor gates on a semiconductor substrate, wherein each of the gates comprises a silicon nitride insulator above a polysilicon gate electrode, b) ion implanting said semiconductor substrate using said gates as a mask to form lightly doped drain regions, c) forming silicon nitride spacers on the sidewalls of each gate, d) forming heavily doped first drain and first source regions in a non-memory region in said substrate using the silicon nitride spacer as a mask, e) forming silicon oxide spacers over said silicon nitride spacers, f) forming heavily doped second drain and second source regions in a memory region in said substrate using said silicon oxide spacers as a mask, g) depositing an interpoly oxide layer over said substrate, h) forming opening in said interpoly oxide layer in said non-memory region, exposing gate sidewall spacers, i) removing said silicon oxide spacers from within said opening j) forming a self aligned contact in said opening. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification