Semiconductor memory capable of being driven at low voltage and its manufacture method
View Patent ↗A gate insulating film is formed in a partial area of the surface of a semiconductor substrate, and on this gate insulating film, a gate electrode is formed. An ONO film is formed on the side wall of the gate electrode and on the surface of the semiconductor substrate on both sides of the gate electrode, conformable to the side wall and the surface. A silicon nitride film of the ONO film traps carriers. A conductive side wall spacer faces the side wall of the gate electrode and the surface of the semiconductor substrate via the ONO film. A conductive connection member electrically connects the side wall spacer and gate electrode. Source and drain regions are formed in the surface layer of the semiconductor substrate in areas sandwiching the gate electrode. A semiconductor device is provided which can store data of two bits in one memory cell and can be driven at a low voltage.
1. A method of manufacturing a semiconductor device, comprising the steps of:
forming a two layer structure comprising a gate insulation film and a gate electrode on a partial area of a surface of a semiconductor substrate;
forming a lamination film on surfaces of the semiconductor substrate, gate insulating film and gate electrode conformable to the surfaces, the lamination film having a structure of at least three layers, each of the three layers being made of insulating material, and a middle layer being made of material easier to trap carriers than other two layers;
forming a conductive side wall spacer on a surface of the lamination film in areas along a side wall of the gate electrode;
etching the lamination film at least to a bottom of the middle layer in an area not covered with the side wall spacers;
implanting first impurities into a surface layer of the semiconductor substrate by using the gate electrode and the side wall spacer as a mask;
forming a first insulating film by locally oxidizing the surface of the semiconductor substrate not covered with the gate electrode and the side wall spacer;
removing an insulating film formed on an upper surface of the gate electrode and on a surface of the side wall spacer; and
forming a connection member electrically connecting the upper surface of the gate electrode and the surface of the side wall spacer.
2. A method according to claim 1 , wherein:
the two layer structure of the gate insulating film and gate electrode extends in a first direction on the surface of the semiconductor substrate and is formed in each of a plurality of areas disposed in parallel to each other; and
said step of forming the connection member comprises:
a step of covering a whole surface of the semiconductor substrate with a conductive film;
a step of patterning the conductive film to leave a plurality of gate lines extending in a second direction crossing the first direction and disposed in parallel to each other;
a step of etching the gate electrode by using the gate lines as a mask after the gate lines are left; and
a step of implanting second impurities of a conductivity type opposite to the first impurities into a surface layer of the semiconductor substrate under an area where the gate electrode was etched.
3. A method of manufacturing a semiconductor device, comprising the steps of:
forming a three layer structure comprising a gate insulation film on a gate electrode and a gate upper film partial area of a surface of a semiconductor substrate;
forming a lamination film of a lower layer, a middle layer and an upper layer, the lower layer covering exposed surfaces of at least the semiconductor substrate, gate insulating film and gate electrode, the middle layer covering surfaces of the lower layer and gate upper film, the upper layer covering the middle layer, each of the lower, middle and upper layers being made of insulating material, and the middle layer being made of material easier to trap carriers than the lower and upper layers;
forming a first conductive film covering a surface of the lamination film;
anisotropically etching the lamination film and first conductive film to leave a side wall spacer, which is made of a portion of the first conductive film, and a portion of the lamination film on a side wall of the gate electrode and gate upper film, and to remove at least the first conductive film and the upper and middle layers of the lamination film on the surface of the semiconductor substrate in an area where the gate electrode is not disposed;
implanting first impurities into a surface layer of the semiconductor substrate by using the gate electrode, gate upper film and side wall spacer as a mask;
forming a second film of insulating material on or over a whole surface of the semiconductor substrate;
polishing the second film until the gate upper film is exposed;
removing the gate upper film and the lamination film left on the side wall of the gate upper film; and
forming a connection member electrically connecting an upper surface of the gate electrode and an exposed surface of the side wall spacer.
4. A method according to claim 3 , wherein:
the three layer structure of the gate insulating film, gate electrode and gate upper film extends in a first direction on the surface of the semiconductor substrate and is formed on each of a plurality of areas disposed in parallel to each other; and
said step of forming the connection member comprises:
a step of covering a whole surface of the semiconductor substrate with a third conductive film;
a step of patterning the third film to leave a plurality of gate lines extending in a second direction crossing the first direction and disposed in parallel to each other;
a step of etching the gate electrode, at least an upper layer of the second film and the side wall spacer by using the gate lines as a mask after the gate lines are left; and
a step of implanting second impurities of a conductivity type opposite to the first impurities into a surface layer of the semiconductor substrate under an area where the gate electrode was etched.