EEPROM CELL WITH THE DRAIN DIFFUSION REGION SELF-ALIGNED TO THE TUNNEL OXIDE REGION AND METHOD OF MANUFACTURE

摘要

A method of semiconductor fabrication, in which a single aperture is used to define both a thin oxide tunneling region and a drain diffusion region in a self-aligned fashion, produces a device structure suitable for use in an electrically-erasable read-only memory (EEPROM) cell. A gate oxide is grown, then a photoresist mask is formed having a slit for ion implantation into the drain diffusion region. The oxide within the slit is etched away, and ion implantations forms a drain diffusion region. After the mask is stripped away, a healing furnace cycle removes the implant damage. A thin tunnel oxide layer is grown over the drain diffusion region, and then a polysilicon floating gate is formed so that one edge of this gate intersects a portion of the area of tunnel oxidation so as to form a small region of tunnel oxide under the floating gate. The process sequence then reverts to a conventional MOS flow. The self-aligned drain diffusion region and tunnel oxide region can be used in a variety of EEPROM cell designs. One embodiment involves a double-polysilicon, single-metal process in which thre diffusion regions are used to form the EEPROM cell. The second layer of polysilicon overlies the floating gate and forms a control gate word line. The control gate and the floating gate overly the channel between the drain diffusion region and a common source diffusion region. The first layer of polysilicon is also used to form a select gate overlying the channel between the drain diffusion region and a select drain diffusion region. The metal layer provides contact to the select drain diffusion region and forms the bit line.