Method for making flash memory

The invention discloses a method for making a flash memory, comprising the steps of providing a semiconductor substrate and performing a well injection process on the semiconductor substrate, forming a gate stack structure on the semiconductor substrate, and performing an injection process to form a source region and a drain region at the two sides of the gate stack structure in the semiconductor substrate. According to the making method of the invention, a cell source and drain (CSD) pocket injection process is employed to replace a traditional gate stack structure threshold voltage injection process, the pocket doping profile is formed based on different thermal diffusion rates of boron ions and arsenic ions, and further, the threshold voltage of the device channel is adjusted. By adopting the making method of the invention, the influence of the heat treatment process to the device channel doping profile is avoided, the channel capacitance is reduced, the programming voltage disturbance (Vpgm disturb) is reduced, and finally, the overall performance and yield of the NAND flash memory are improved.