Strapless Substrate Contact With Double Poly Fill/Diffusion Connection
Original Publication Date: 1988-Apr-01
Included in the Prior Art Database: 2005-Feb-15
A two-step polysilicon fill process is described to form a semiconductor substrate contact through the trench of a static or dynamic random access memory cell (SRAM or DRAM, respectively). In a new CMOS memory cell substrate contact structure, a strap and strap contact is eliminated by integrating the substrate contact in silicon. To form the substrate contact through a memory cell trench, the trench is etched, as shown in the figure, and lined with oxide and nitride insulators. The floor of the cell is etched away using existing reactive ion etch processes and the trench is polysilicon filled . After trench surface planarization, a portion of the trench is removed. This includes single crystal silicon adjacent to the trench, polycrystal (trench fill) and the dual wall insulator.