Three-dimensional memory device including discrete charge storage elements and methods of forming the same
A method of forming a memory device includes forming an alternating stack of disposable material layers and silicon nitride layers over a substrate, forming a memory opening through the alternating stack, forming a memory film and a vertical semiconductor channel in the memory opening, where the memory film includes a continuous silicon nitride charge storage material layer and a tunneling dielectric layer, forming a backside trench through the alternating stack, forming laterally-extending cavities by removing the disposable material layers selective to the silicon nitride layers through the backside trench, oxidizing portions of the silicon nitride layers and the continuous silicon nitride charge storage material layer exposed in the laterally-extending cavities to form silicon oxide insulating layers and to separate the continuous silicon nitride charge storage material layer into a vertical stack of discrete silicon nitride charge storage material portions, and replacing remaining portions of the silicon nitride layers with electrically conductive layers.
1 . A method of forming a memory device, comprising:
forming an alternating stack of disposable material layers and silicon nitride layers over a substrate;
forming a memory opening through the alternating stack;
forming a memory film and a vertical semiconductor channel in the memory opening, wherein the memory film comprises a continuous silicon nitride charge storage material layer and a tunneling dielectric layer;
forming a backside trench through the alternating stack;
forming laterally-extending cavities by removing the disposable material layers selective to the silicon nitride layers through the backside trench;
oxidizing portions of the silicon nitride layers and the continuous silicon nitride charge storage material layer exposed in the laterally-extending cavities to form silicon oxide insulating layers and to separate the continuous silicon nitride charge storage material layer into a vertical stack of discrete silicon nitride charge storage material portions, wherein a horizontally-extending seam is formed in each of the silicon oxide insulating layers during the oxidation; and
replacing remaining portions of the silicon nitride layers with electrically conductive layers.
2 . The method of claim 1 , wherein:
the portions of the continuous silicon nitride charge storage material layer that are exposed in the laterally-extending cavities are converted into a vertical stack of annular silicon oxide material portions during the oxidizing; and
the vertical stack of discrete silicon nitride charge storage material portions is interlaced with the vertical stack of annular silicon oxide material portions along a vertical direction.
3 . The method of claim 1 , wherein the portions of the silicon nitride layers that are exposed in the laterally-extending cavities are converted into silicon oxide material portions that expand in volume to fill the laterally-extending cavities.
4 . The method of claim 3 , further comprising laterally recessing the silicon oxide material portions, wherein remaining parts of the silicon oxide material portions that fill the laterally-extending cavities comprise the silicon oxide insulating layers.
5 . The method of claim 1 , wherein the memory film further comprises a blocking dielectric layer.
6 . The method of claim 1 , further comprising removing portions of the blocking dielectric layer exposed in the laterally-extending cavities, wherein remaining portions of the blocking dielectric layer comprise a vertical stack of tubular insulating spacers.
7 . A method of forming a memory device, comprising:
forming an alternating stack of disposable material layers and silicon nitride layers over a substrate;
forming a memory opening through the alternating stack;
forming a memory film and a vertical semiconductor channel in the memory opening, wherein the memory film comprises a continuous silicon nitride charge storage material layer and a tunneling dielectric layer;
forming a backside trench through the alternating stack;
forming laterally-extending cavities by removing the disposable material layers selective to the silicon nitride layers through the backside trench;
oxidizing portions of the silicon nitride layers and the continuous silicon nitride charge storage material layer exposed in the laterally-extending cavities to form silicon oxide insulating layers and to separate the continuous silicon nitride charge storage material layer into a vertical stack of discrete silicon nitride charge storage material portions; and
replacing remaining portions of the silicon nitride layers with electrically conductive layers, wherein the replacing the remaining portions of the silicon nitride layers with the electrically conductive layers comprises selectively removing the remaining portions of the silicon nitride layers through the backside trench to form backside recesses, recessing the silicon oxide insulating layers to remove a bird's beak, and forming the electrically conductive layers in the backside recesses through the backside trench.
8 . The method of claim 1 , wherein an air gap is formed in each of the silicon oxide insulating layers during the oxidation.
9 . The method of claim 1 , wherein the oxidizing comprises a high pressure oxidation step in a water vapor ambient at a pressure of at least 10 atm and a temperature of at least 750 degrees Celsius.