Three dimensional memory
A method to fabricate a three dimensional memory structure may include creating a stack of layers including a conductive source layer, a first insulating layer, a select gate source layer, and a second insulating layer, and an array stack. A hole through the stack of layers may then be created using the conductive source layer as a stop-etch layer. The source material may have an etch rate no faster than 33% as fast as an etch rate of the insulating material for the etch process used to create the hole. A pillar of semiconductor material may then fill the hole, so that the pillar of semiconductor material is in electrical contact with the conductive source layer.
1. A method to fabricate a three dimensional memory structure comprising
creating a conductive source layer comprising a source material,
creating an insulating layer above the conductive source layer, the insulating layer comprising an non-conductive material,
creating a select gate source layer above the insulating layer,
forming an array stack above the select gate source layer,
using the conductive source layer as a stop-etch layer to create a hole through the array stack, the select gate source layer, and the first insulating layer, that stops in the conductive source layer, and
creating a pillar of semiconductor material in the hole, the pillar of semiconductor material in electrical contact with the conductive source layer,
wherein the source material has an etch rate no faster than 33% as fast as an etch rate of the non-conducting material for an etch process used to create the hole.
2. The method of claim 1 , wherein the source material comprises a metallic silicide.
3. The method of claim 1 , wherein the source material comprises tungsten silicide.
4. The method of claim 1 , further comprising
heavily doping the source material with arsenic or phosphorus,
wherein the electrical contact between the pillar of semiconductor material and the conductive source layer comprises an ohmic contact.
5. The method of claim 1 , wherein the select gate source layer, and the pillar of semiconductor material comprise polysilicon, and the insulating layer comprises silicon oxide.
6. The method of claim 1 , further comprising
creating a select gate drain layer above the array stack before the creation of the hole,
wherein the hole is also created through the select gate drain layer.
7. The method of claim 1 , further comprising
forming charge storage mechanisms in the hole before creating the pillar of semiconductor material,
wherein a charge storage mechanism comprises a conductive floating gate or a non-conductive charge trapping layer.
8. The method of claim 1 , further comprising
depositing one or more films inside the hole, and
etching inside the hole for one or more periods.
9. The method of claim 1 , wherein the creating of the hole is accomplished by a single dry etch process.
10. The method of claim 1 , wherein a depth of the hole is at least 10 times as deep as a width of the hole.
11. The method of claim 1 , further comprising patterning the conductive source layer.