MOS device structure and integration method

A method of making MOS devices with salicided gate and source and drain, comprising the steps of

• a. forming a pattern of field oxide on a silicon substrate using LOCOS;
• b. thermally growing a gate oxide layer on the silicon substrate in the active area defined by the field oxide window;
• c. depositing a layer of polysilicon over the substrate;
• d. depositing a layer of photoresist over the polysilicon, exposing the photoresist through a gate definition mask, developing the photoresist;
• e. anisotropically reactive-ion etching the polysilicon and the gate oxide to form the polysilicon gate and the gate oxide, followed by the removal of the photoresist;
• f. covering the substrate with a layer of silicon nitride by chemical vapor deposition;
• g. anisotropically reactive-ion etching the silicon nitride to the end point defined by the exposure of the silicon substrate, thus forming the gate's first sidewall spacer of silicon nitride;
• h. then conformally depositing a layer of amorphous silicon over the topography of the silicon substrate, and defining the pattern using an active region definition mask;
• i. implanting nitrogen into the amorphous silicon layer whereby as a result, nitrogen piles up at the interface between the native oxide layer on the amorphous silicon layer and the amorphous silicon layer in the gate and the source and drain areas where the surface of the amorphous silicon layer is perpendicular to the nitrogen ion beam;
• j. thermally oxidizing the amorphous silicon in the sidewall areas not implanted with nitrogen to form the gate's second sidewall of silicon dioxide;
• k. implanting dopant into the amorphous silicon layer;
• l. converting the amorphous silicon into polysilicon layer by annealing;
• m. annealing to drive some implanted dopant into the single silicon substrate in the source and drain area to form shallow junctions, as well as into the polysilicon gate;
• n. depositing a layer of refractory metal on polysilicon layer, followed by a first rapid thermal annealing to form silicide of the refractory metal;
• o. removing the unsilicided metal covering the areas of field oxide and gate sidewall oxide;
• and
• p. a second rapid thermal annealing to improve the conductivity of the silicide.