| 摘要 |
PURPOSE:To constitute a four-value memory having planar cell structure wherein the fluctuation of ON current is suppressed in each memory element. CONSTITUTION:In order to form a memory element 12a of first state for a silicon wafer on which memory elements of planar cell structure are formed, a resist pattern 26 having an opening 24a including the entire channel region is formed and used as a mask when boron ions are implanted into the substrate through a word line 6. In order to form a memory element 12b of second state and a memory element 12c of third state, a resist pattern 28 having an opening 24b including the entire channel region and an opening 24c including one side part of channel width are then formed and used as a mask, along with a word line 6, when borons are implanted into the surface of substrate at an inclination of 30-60 deg. from the vertical direction, i.e., by oblique rotary ion implantation. It is then heat treated so that the impurities are diffused from the side part thus forming a diffused region extending by about one third of the channel width. |
