Nanocrystal memory with differential energy bands and method of formation
View Patent ↗A method of making a semiconductor device using a semiconductor substrate includes forming a first insulating layer having a first band energy over the semiconductor substrate. A first semiconductor layer having a second band energy is formed on the first insulating layer. The first semiconductor layer is annealed to form a plurality of first charge retainer globules from the first semiconductor layer. A first protective film is formed over each charge retainer globule of the plurality of first charge retainer globules. A second semiconductor layer is formed having a third band energy over the plurality of first charge retainer globules. The second semiconductor layer is annealed to form a plurality of storage globules from the second semiconductor layer over the plurality of first charge retainer globules. A magnitude of the second band energy is between a magnitude of the first band energy and a magnitude of the third band energy.
1. A semiconductor memory device, comprising:
a semiconductor substrate;
a first insulating layer having a first energy band over the semiconductor substrate;
a plurality of nanocrystals on the first insulating layer, wherein each nanocrystal comprises:
a first charge retainer globule having a second energy band over the first insulating layer;
a first protective film over the first charge retainer globule;
a storage globule having a third energy band over the first protective film, wherein a magnitude of the second energy band is between a magnitude of the first energy band and a magnitude of the third energy band; and
a second insulating layer over the plurality of nanocrystals; and
a gate over the second insulating layer.
2. The semiconductor memory device of claim 1 , wherein each nanocrystal further comprises:
a second protective film over the storage globule; and
a second charge retainer globule having a fourth energy band over the storage globule, wherein the second insulating layer has a fifth energy band and a magnitude of the fourth energy band is between the magnitude of the third energy band and a magnitude of the fifth energy band.
3. The semiconductor memory device of claim 1 , wherein:
the first energy band comprises a first conduction energy band;
the second energy band comprises a second conduction energy band;
the third energy band comprises a third conduction energy band;
the substrate comprises silicon;
the first insulating layer comprises oxide;
the first charge retaining globule comprises p-doped silicon; and
the first storage globule comprises n-doped silicon.
4. The semiconductor memory device of claim 1 , wherein:
the first energy band comprises a first conduction energy band;
the second energy band comprises a second conduction energy band;
the third energy band comprises a third conduction energy band;
the first storage globule comprises one of a group consisting of silicon germanium and germanium; and
the first charge retaining globule comprises silicon.
5. The semiconductor memory device of claim 1 , wherein:
the first energy band comprises a first valence energy band;
the second energy band comprises a second valence energy band;
the third energy band comprises a third valence energy band;
the substrate comprises silicon;
the first insulating layer comprises oxide;
the first charge retaining globule comprises n-doped silicon; and
the first storage globule comprises p-doped silicon.
6. A method of forming a nanocrystal over an insulating layer, wherein the insulating layer has a first band energy, comprising:
forming a charge retaining globule having a second band energy;
growing an oxide layer around the charge retaining globule; and
forming a charge storage globule over the oxide layer, wherein the charge storage globule has a third band energy, wherein the second band energy has a magnitude that is between a magnitude of the first band energy and a magnitude of the third band energy.
7. The method of claim 6 , wherein:
forming the charge retaining globule further comprises forming a semiconductor globule doped to a first doping type; and
forming the charge storage globule further comprises forming a semiconductor globule doped to a second doping type opposite to the first doping type.