Methods and apparatus for three dimensional NAND structure fabrication

1. A method for forming a plurality of nonvolatile memory cells, comprising:

forming, on a substrate, a stack of alternating layers of metal including a first layer of metal and a second layer of metal different from the first layer of metal;

removing the first layer of metal to form spaces between the alternating layers of the second layer of metal;

one of depositing a first layer of material to partially fill the spaces to leave air gaps therein or depositing a second layer of material to fill the spaces;

forming at least one memory hole in the stack of alternating layers of the first layer of metal, the second layer of metal, and a layer of silicon nitride (SiN) and poly-silicon (poly-Si) on which the first layer of metal is deposited; and

depositing in the at least one memory hole:

a layer of aluminum oxide (AlO);

a first layer of silicon oxide atop the layer of AlO;

a layer of SiN atop the first layer of silicon oxide;

a second layer of silicon oxide atop the layer of SiN;

a layer of poly-Si atop the second layer of silicon oxide to form a poly-Si channel; and

a core silicon oxide to fill the poly-Si channel.

2. The method of claim 1 , wherein the one of depositing the first layer of material to partially fill the spaces to leave air gaps therein or depositing the second layer of material in the spaces is performed using one of chemical vapor deposition or atomic layer deposition.

3. The method of claim 1 , wherein the first layer of metal and the second layer of metal are deposited using at least one of chemical vapor deposition and physical vapor deposition.

4. The method of claim 1 , wherein removing the first layer of metal is performed using one of: a dry chemical etch process containing F chemistries comprising fluorine compounds including at least one of SF 6 , CF 4 , CHF 4 , CH 3 F, C 2 F 6 , C 4 F 8 , or NF 3 ; or a wet etch process.

5. The method of claim 1 , wherein forming the at least one memory hole is performed using a dry chemical etch process containing F chemistries comprising fluorine compounds including at least one of SF 6 , CF 4 , CHF 4 , CH 3 F, C 2 F 6 , C 4 F 8 , or NF 3 .

6. The method of claim 1 , further comprising, prior to removing the first layer of metal to form spaces between the alternating layers of the second layer of metal:

forming at least two slits through the first layer of metal, the second layer of metal, and the layer of SiN and poly-Si using F-based chemistry comprising fluorine compounds including at least one of SF 6 , CF 4 , CHF 4 , CH 3 F, C 2 F 6 , C 4 F 8 , or NF 3 ;

removing the layer of SiN and poly-Si from the substrate using one of a wet etch process or chemical dry etch process;

removing, from the at least one memory hole in an area that was occupied by the layer of SiN and poly-Si prior to removal thereof, the layer of AlO, the first layer of silicon oxide atop the layer of AlO, the layer of SiN atop the first layer of silicon oxide, and the second layer of silicon oxide atop the layer of SiN using a chemical dry etch process; and

depositing a layer of phosphorous doped poly-Si on the substrate in place of the removed layer of AlO, the removed first layer of silicon oxide, the removed layer of SiN, and the removed second layer of silicon oxide to cover a portion of the poly-Si channel.

7. The method of claim 6 , further comprising, subsequent to removing the first layer of metal to form spaces between the alternating layers of the second layer of metal and prior to one of depositing the first layer of material to partially fill the spaces to leave air gaps therein or depositing the second layer of material to fill the spaces:

removing, from the at least one memory hole in an area that was occupied by the layer of first metal prior to removal thereof, the layer of AlO, the first layer of silicon oxide atop the layer of AlO, and the layer of SiN atop the first layer of silicon oxide using the chemical dry etch process.

8. The method of claim 1 , wherein the first layer of metal is at least one of tungsten (W), molybdenum (Mo), tantalum (Ta), niobium (Nb), osmium (Os), zirconium (Zr), iridium (Ir), rhenium (Re), titanium (Ti), Ti nitride (TiN), TaN, WN, MoN, ZrN, WOx, RuOx, and IrOx,

wherein the second layer of metal is one of W, Mo, Ta, Ru, Nb, Os, Zr, Ir, Re, and Ti,

wherein the first layer of material is silicon oxide, and

wherein the second layer of material is a low k oxide.

9. The method of claim 8 , wherein the low k oxide is one of silicon oxide or silicon dioxide having a dielectric constant that is less than or equal to 3.9.