| abstract |
A CMOS memory device includes source and drain regions diffused into a substrate, a polysilicon gate structure formed over a channel region located between the first and second diffusion regions, and a pre-metal dielectric structure formed over the polysilicon gate structure. The pre-metal dielectric structure is a triple layer structure including a lower Borophosphosilicate glass (BPSG) layer formed over the polysilicon gate structure, a Nitride layer formed on the lower BPSG layer, and an upper dielectric layer (e.g., BPSG or USG) formed on the Nitride layer. The Phosphorous concentration in the lower BPSG layer is greater than the Phosphorous concentration in the upper dielectric layer, thereby providing retention protection for the underlying memory structures while facilitating optimal chemical mechanical polishing (CMP) planarization characteristics. The Nitride layer acts as a barrier to impede the migration of Phosphorous from the lower BPSG layer to the upper dielectric layer, and to prevent the migration of impurities from the upper dielectric layer to the lower dielectric layer that are introduced during CMP planarization. |